Could more fuel-efficient engines lead to more global warming?


Auto industry experts predict that more than 50 percent of cars on the road by 2020 will use a relatively new type of fuel-efficient engine. This transition, however, has raised questions about its ultimate effect on the climate. A study published in ACS’ journal Environmental Science & Technology has found that because the newer engines emit higher levels of the climate-warming pollutant black carbon than traditional engines, their impact on the climate is uncertain.

Naomi Zimmerman and colleagues analyzed four scenarios based on reported black carbon emissions from both traditional port fuel injection engines and newer gasoline direct injection (GDI) engines. They determined that installing efficient particulate filters in vehicles with GDI engines — even if they slightly lower fuel efficiency — could likely balance this trade-off and benefit the climate. But this outcome is not a given and depends on a variety of factors that can impact black carbon emissions such as engine design, fuel composition and geographic location.

Cars with newer gasoline direct injection (GDI) engines emit more black carbon than those with traditional port fuel injection (PFI) engines, but installing filters could mitigate this. CREDIT American Chemical Society

Cars with newer gasoline direct injection (GDI) engines emit more black carbon than those with traditional port fuel injection (PFI) engines, but installing filters could mitigate this. CREDIT American Chemical Society


The paper:

Assessing the Climate Trade-Offs of Gasoline Direct Injection Engines

Naomi Zimmerman, Jonathan M. Wang, Cheol-Heon Jeong, James S. Wallace, and Greg J. Evans


Compared to port fuel injection (PFI) engine exhaust, gasoline direct injection (GDI) engine exhaust has higher emissions of black carbon (BC), a climate-warming pollutant. However, the relative increase in BC emissions and climate trade-offs of replacing PFI vehicles with more fuel efficient GDI vehicles remain uncertain. In this study, BC emissions from GDI and PFI vehicles were compiled and BC emissions scenarios were developed to evaluate the climate impact of GDI vehicles using global warming potential (GWP) and global temperature potential (GTP) metrics. From a 20 year time horizon GWP analysis, average fuel economy improvements ranging from 0.14 to 14% with GDI vehicles are required to offset BC-induced warming. For all but the lowest BC scenario, installing a gasoline particulate filter with an 80% BC removal efficiency and <1% fuel penalty is climate beneficial. From the GTP-based analysis, it was also determined that GDI vehicles are climate beneficial within <1–20 years; longer time horizons were associated with higher BC scenarios. The GDI BC emissions spanned 2 orders of magnitude and varied by ambient temperature, engine operation, and fuel composition. More work is needed to understand BC formation mechanisms in GDI engines to ensure that the climate impacts of this engine technology are minimal.

177 thoughts on “Could more fuel-efficient engines lead to more global warming?

    • Perhaps ‘Black Carbon Matters’ is equivalent to Black Lives Matter. Let the search for White Carbon begin!

    • NW sage —
      SMC —
      “Black Carbon Matters” — Wish I had said that — Eugene WR Gallun

    • Fuel efficient engines reduce drastically the health hazardous gases, more particularly Asthma causing affect will be down. BC is not a greenhouse gas but on the contrary its life is short and falls on to the ground in summer and washed away in rainy season. Wind & greenery plays important role.
      In Indian cities it is different as fuel is mixed with like kerosene. The roads are narrow and thus slow motion creates burning of fuel problem. Added to this is buring of garbage “domestic waste” in open all around.
      Dr. S. Jeevananda Reddy

      • Fuel efficient petrol cars with direct injection emit more of the most dangerous small particles (PM2.5), so they’re definitely a health problem. Mandatory particle filters like on Diesel engines will inevitably come.

      • Also the issue is in winter, when the black soot lands on snow, it will cause it to melt faster, lowering the Earth’s albedo a bit, and increasing the rate of snow melt. We are already blaming soot like particles on the extra Greenland ice melt, if you believe that is really happening.

      • Bryan A
        July 14, 2016 at 12:08 pm
        Some of the effects of Black Carbon would be Dark Snow
        According to the ‘Dark Snow’ Project, author of the video, much of that black material is cyanobacteria and blue-green algae.

      • As long as the vehicle moves in the normal speed, it is not a problem — release of PM2.5. At higher latitudes the day length changes — snow areas around 6 months no sunlight. When we look at integrated condition — including general circulation patterns and climate system, fuel efficient cars/vehicles are less health hazardous over the non-fuel efficient cars/vehicles.
        Dr. S. Jeevananda Reddy

      • @Espen;
        The actual effects of PM2.5 remain, to put it generously, uncertain. The next study to provide solid evidence (pun intended) will be the first.

      • The snow might not even be there if it wasn’t for the soot.
        Soot particles act as substrates for water droplets to form on which ultimately can become snow crystals and precipitate out on the ground. Naturally, each snow crystal will have a soot particle inside. Within about 72 hours, assuming that this place does get some daylight, that pristine snow surface will have melted and refroze at least once and the soot particles will start to be exposed.
        Better to have sooty snow, than no snow at all.

        • Besides that, we can just change the color of the BC particles to white, and all go home happy! Just don’t tell BLM (the movement, not the agency) of they’ll scream “Dog whistle!” and my hearing is bad enough as it is.

    • Well my first objection to the essay is the statement that the newer direct fuel injection (similar to diesel injection) , which are more efficient than the “traditional” port fuel injection engines, emit more black carbon.
      Poppycock; direct fuel injection WAS the traditional fuel injection process used in (some) gasoline engines, and yes it is way more fuel efficient.
      The “traditional” port fuel injection; more properly termed a pressurized carburetor system, was a more recent cost cutting measure.
      How do I know this ? Many years ago, circa mid-late 1970s, I purchased a Porsche 911T (not Targa) Coupe (not ragtop). It was a special mustard color paint job and was a dealer demo (aka used car) with about 4-500 miles on it. I believe I paid $9,000 for it.
      Actually now that I remember I was actually leasing it; but $9k was the end cost of the deal.
      So after doing the paper work, I hopped in my fancy new machine, and drove it out of the dealer’s lot.
      There was a sudden sounding of bells and whistles and fireworks going off as I got to the street. So what happened ?
      My dealer Demo, was the very last of that particular model Porsche available in the State of California, and was now obsolete replaced by a whizz bang brand new model.
      And the price for the new and improved model was increased by $1,000 over last year’s model, but my obsolete model was worth an additional $1,000 on the market.
      Whyzatt ??
      The reason was my car had the “traditional” high pressure direct fuel injection into the cylinder engine; but the new and improved model had the pressurized carburetor engine, where instead of the intake manifold vacuum sucking gas out of the carburetor jets into the intake port, like all ordinary cars do, a controllable “injector” blew a shot of gas into the intake manifold instead.
      Traditional” direct high pressure injection into the cylinder, in gasoline engines goes back to at least 1954.
      Well that was the year that Juan Manuel Fangio cleaned up the formula one GP circuit big time driving the Mercedes W-196 car, which had direct high pressure fuel injection, which works pretty much the same as in diesel engines, except the gas ones still have a spark ignition system.
      So these newfangled super cars are just old fashioned as heck.
      I’m sure that engineengineers have learned a lot about DHPFI over the years, so these new ones will likely be very good.
      As to the black carbon emissions; more black carbon means more water droplets nucleated so that’s a good thing. But more soot which is the technical term for black carbon, also means the efficiency is not as good as it could be when they get the stoichiometry correct, so that the soot gets burned up too.
      It’s not fuel efficient to add water to the gasoline which is what alcohol or ethers do, but it is also not fuel efficient to burn a hydrocarbon fuel and end up with carbon instead of CO2.
      PS. I drove my Real fuel injected Porsche for three years on that lease, and then sold it. I got all of my money back plus $300 because that car really was fuel injected.

      • Your Porsche’s mechanical Fuel injection was still “PFI” (Port Fuel Injection). Fuel was sprayed outside the combustion chamber. Almost all “performance cars” since the mid 1980’s have used Electronic PFI, while trucks and non performance cars received Throttle Body Injection (TBI) which is a fuel injection carburetor, which where generally fazed out in favor of PFI during the 1990’s, Since about 2000 virtually every gasoline car on the road is PFI. Until the last 10 or so years only Diesels were DI.
        A mechanical Injection Porsche or Ferrari from the 1960’s/1970’s had 200-300 PSI fuel pressure. No way is this enough for GDI, Even a lowly Kia GDI pump supplies fuel at 10X this pressure.
        1970’s Porsche Fuel injection was “ahead of its time”, but that time was 1985, not 2016.

      • Well the Wattsupwiththat Engine design team are already working on solving the problem by the look of this thread.
        So keep at it chaps; there’s more commonsense heads on this blog, than you can assemble anywhere on the planet.
        I’m thinking some sort of high pressure direct fuel injected turbo supercharged two stroke gasoline engine, is the best way to go for weight and size and power and efficiency, and the soot is just more fuel to burn in the engine.

    • Ah, Black Carbon collects on sea ice causing it to melt, causing sea level rise, causing the thermohaline circulation to stop, causing the end of the world as we know it. So of course it must be a climate warming pollutant. 🙂

  1. not to worry: CARB will demand that the exhaust be modified to capture all the black carbon…
    the fact that this will double the cost of the vehicle won’t bother them at all.

      • “particulate filters not expensive”
        What’s the maintenance schedule / service cost on those?

      • The problem with particulate filters is the obsession with ‘zero maintenance’ vehicles. This demands that the filter be put near the manifold end, so that carbon can be burned off with the help of special additives. This arrangement is also wasteful of fuel and bad for the engine, since it causes oil dilution with unburned fuel.
        The sensible arrangement would be for the filter to be the last item on the exhaust, such that the owner can take it off and pressure wash it when it starts to clog. Of, for those owners who absolutely cannot manage even this simple task, I’m sure the fast-fit outlets would soon take advantage of the market for providing a while-you-wait filter hosedown.

  2. “black carbon, a climate warming pollutant” Precisely how is it that they KNOW that both statements are always true? Black carbon is climate warming? True, false, always, sometimes, under what other conditions?
    Black carbon is a pollutant? True, false, always sometimes, under what conditions? and how is ‘pollutant’ defined? and does that definition fit the real world and make any sense?

      It depends on what you want it to do.
      ‘If black carbon heats up the layer of the atmosphere where clouds are forming, for example, they will evaporate. They can no longer reflect sunlight back into space, and so the soot-laced clouds end up warming the atmosphere. But black carbon that hangs above low-lying stratocumulus clouds has a different effect. It stabilizes the layer of air on top of the clouds, promoting their growth. It just so happens that thick stratocumulus clouds are like shields, blocking incoming sunlight. As a result, black carbon also ends up cooling the planet.’

      • If black carbon heats up the layer of the atmosphere where clouds are forming, for example, they will evaporate.
        What a stupid comment! If black carbon is present in a cloud forming layer it will increase the cloud formed by acting as a nucleation center for the saturated air.

      • I don’t think it’s so simple, Liar
        A NAVY chemist has proved that carbon black can make or break a cloud. She is
        Florence W. van Straten, now working with the Navy Weather Service.
        What van Straten’s discovery means in terms of scientific weather control is now being measured by Naval Research Laboratory. But she has already demonstrated that carbon black, absorbing heat from the sun, can change atmospheric conditions enough to create clouds or to break them up quickly.
        For some time, van Straten believed she could modify clouds by influencing temperatures in parts of the atmosphere. In this manner, she says, cloud masses that exist could be dissipated, and, under some conditions, cloud masses could be created. She reasoned further that carbon black would be the ideal material to induce the temperature variations because of its ability to absorb heat.
        Chem. Eng. News, 1958, 36 (40), pp 67–68
        DOI: 10.1021/cen-v036n040.p067
        Publication Date: October 06, 1958

  3. Hey, finally, something without coal that has actual carbon emissions! Black Carbon is different from carbon dioxide. BC is a direct hazard to health from inhalation and effects on the lungs- asthma, COPD, loss of effective lung volume, and possible direct toxic effects.

    • Alll small particulates are dangerous – these include talcum powder and face powder which have very small particulates and which should of course be banned immediately.

      • “Alll small particulates are dangerous”
        How about very finely divided platinum and similar?
        “French firm Veolia is recycling precious metals worth 100,000 pounds ($155,000) each year from dust swept off British streets and plans to recover more by opening two new plants.
        Every day, catalytic converters in cars spit out minute particles of platinum, palladium and rhodium, which end up in road sweepings gathered by waste recyclers like Veolia.
        In the past year, Veolia Environnement’s pilot plant in Ling Hall, close to the central English city of Birmingham, has started to filter out these precious metals from the 40,000 tonnes a year of dust it treats.”
        Worth mentioning also that that 40,000 tonnes of dust is composed of tyre rubber – which contains considerable quantities of carbon and all sorts of other good stuff, brake lining and disc brake dust and asphalt particles.
        Interesting also is that it appears that hybrid and electric cars produce more tyre and brake dust per mile because they are heavier than similar classes of fossil fuelled vehicles.

      • I see ambulance chaser ads on TV alleging talcum or “baby powder” causes cervical cancer. Why didn’t I think of that?

  4. I thought Black Carbon was a sign of incomplete combustion, and GDI was supposed to improve fuel efficiency. This doesn’t make sense.

    • Perhaps the gasoline doesn’t have time to completely evaporate or (more likely) mix with the combustion air.
      I don’t understand what it is about GDI that makes it more efficient, assuming that it is.

      • GDI allows the state transformation of the liquid fuel to take place within the combustion chamber, thereby reducing the temperature prior to ignition. A cooler combustion chamber leads to the ability to increase the combustion ratio, timing and all those good things that help booste power per unit of fuel. This leads to greater fuel efficiency.
        But I do not know if this leads to unburned fuel which I guess would lead to the particulates and wasted fuel which then leads to reduced fuel economy. My head is spinning now!
        I assumed the substance emitted would be hydrocarbons, not pure carbon. Help someone explain all of this better!

      • “I don’t understand what it is about GDI that makes it more efficient, assuming that it is.”
        The advantage of direct injection is that it allows a much higher compression ratio to be used hence a much higher charge temperature to be achieved before the combustion takes place. That is why diesel engines are considerably more efficient than petrol engines and also burn a much less refined fuel – my somewhat elderly Mercedes runs very well on straight vegetable oil, for example.
        Why the motor industry has suddenly decided to use direct injection on petrol engines is not clear, nor is the reason that the combustion should be less complete than achieved with indirect injection, as there is much more control over fuel distribution, for example it is possible to arrange a richer mixture in the vicinity of the ignition device to initiate combustion of the leaner mixture, as in stratified charge engines, for example.
        I would suspect it is just another way of squeezing more guilt tax out of the motorist, were I of a suspicious nature…

      • It’s the direct fuel injection into the cylinder that makes it more fuel efficient. It could be even more efficient when tey get the combustion chemistry correct and burn the BC to CO2.
        Diesels have a bit more of a problem with BC because they don’t have spark ignition, so they have much higher pressure and Temperature to self ignite, so the combustion process is much more restrictive as to degrees of freedom of the chemistry.
        A regular electric spark ignited engine, should have more degrees of freedom to get the combustion chemistry right so they don’t leave unburned carbon.

      • no fuel droplets “sticking” to intake runners. even injected intakes that were ported and polished were not as efficient due to intake to head interface and gasket interference.
        less mix swirl issues caused by intake valves.
        ability to change mix ratio much faster and with less trim (as read by o2 sensor banks) range needed
        higher compression w/o having to retard timings w/o as many heat issues as port injected has at same compression levels.

    • I’m with Slywolfe. Very sure unburned carbon means poor combustion and less energy in most cases. So what is so different in direct injection? Someone here must know. Without sarcasm this site has SOOO many truly knowledgeable folks.

      • Hi I’ll repost under your thread! GDI allows the state transformation of the liquid fuel to take place within the combustion chamber, thereby reducing the temperature prior to ignition. A cooler combustion chamber leads to the ability to increase the combustion ratio, timing and all those good things that help booste power per unit of fuel. This leads to greater fuel efficiency.
        But I do not know if this leads to unburned fuel which I guess would lead to the particulates and wasted fuel which then leads to reduced fuel economy. My head is spinning now!
        I assumed the substance emitted would be hydrocarbons, not pure carbon. Help someone explain all of this better!

      • The majority of the energy obtained from burning hydrocarbons is actually from the hydrogen combustion, not the carbon combustion. GDI engines apparently emit much less “organic carbon” – i.e. carbon-hydrogen compounds, which appears to mean that they combust more of the hydrogen that is in the fuel.
        Now just why they would combust less of the carbon – that I have no good answer for. Chamber temperature that allows more of the carbon to remain in various molecular forms that are harder to break apart?

      • “Mario Lento July 13, 2016 at 6:11 pm
        GDI allows the state transformation of the liquid fuel to take place within the combustion chamber, thereby reducing the temperature prior to ignition.”
        My understanding, albeit dated now, is that the temperature of the air being drawn in to the combustion changer is what increases the combustion potential, not the fuel that is injected. Cold, denser air, has more mass, hence inter-coolers, with cold water sprays systems, on turbocharged engines or when running old cars normally aspirated with carburetors on a cold damp day always seem to perform better.

      • Right on Patrick.
        My 1st ever new car was a Model 1500 VW bug …. and on a cool damp evening/nighttime that engine produced a lot more HP.

      • Amorphous black carbon is a trade-off in overall engine emissions. Black carbon requires high temperatures to achieve combustion. High combustion temperatures produce much higher emissions of nitrogen oxide compounds which are considered much greater pollutants. Its news to me that amorphous black carbon is a great health hazard. Talc on the other hand has been long known to contribute to health issues.

      • Reality Observer: “The majority of the energy obtained from burning hydrocarbons is actually from the hydrogen combustion, not the carbon combustion. ”
        But H2O vapor is ~8 times a more potent GHG than CO2. Being created from ancient sequestered hydrogen and not from evaporation of existing surface water it will upset the delicate “balance” (**- see below) of natural water vapor concentration .. we’re all doomed!

    • It may be true in some regulatory, through the looking-glass, world. But the ACS has gargled the KoolAid, so anything is possible.

  5. “fuel composition and geographic location”???? More boutique fuels? The word cluster comes to mind.

  6. Black carbon directed onto a road surface is not likely to remain in the atmosphere very long, and carbon that precipitates quickly on icy roadways could improve traction and prevent loss of control, reducing the need for fuel-guzzling emergency vehicles.
    More extensive modeling is needed to examine possible climatic upsides to GDI.

    • Clearly we need to redirect grants to this man out of the CAGW slushfund budget. Ground breaking stuff and it should have further implications for muddy, unsealed roads later on no doubt. We at Black Tar Matters are right behind you sir.

  7. This is masking some facts. GDI engines are diesel. Comparing to petrol/gasoline. All newer engines have a catalysers and particulate filters. Diesels are hated by poltitico’s. I see little gain in wondering about this.

      • … running gasoline as direct injection. What sense does that make?

        It makes a lot of sense to my inner hotrodder. Here’s an article. Port injection is cheaper, so that’s why it is commonly used. If you wanted to be really fast, direct injection was the way to go.
        The trade-offs in engine design are mind numbing. Sometimes you want an intercooler to cool off the air so you can jam more of it into the cylinder. Elsewise, you may want to heat the air to promote better fuel-air mixing.
        With regard to black carbon, also known as soot … Automobiles since the 1970s have had catalytic converters. Unless the engine is badly out of tune, the catalytic converter takes care of the soot and other unburned carbon compounds by oxidizing them. In that regard, direct injection or port injection is a complete red herring.

      • “By putting the injector inside the cylinder, the engine’s computer gains even more precision control over the amount of fuel during the intake stroke, further optimizing the air/fuel mixture to create a clean burning explosion with very little wasted fuel and increased power delivery.
        A GDI system also has more flexibility regarding when in the combustion cycle the fuel is added. MPFI (multi port fuel injection) systems can only add fuel during the intake stroke of the piston, when the intake valve is open. GDI can add fuel whenever it needs to. For example, the some GDI engines can adjust the timing so that a smaller amount of fuel is injected during the compression stroke, creating a much smaller, controlled explosion in the cylinder. This so-called ultra lean burn mode sacrifices a bit of outright power, but greatly reduces the amount of fuel used during times when the vehicle requires very little grunt (idling, coasting, decelerating, etc.).
        GDI engines also react more quickly to these changes in timing and amount of fuel addition, increasing driveability. Additionally, the vehicle is able to more quickly adjust based on inputs from sensors located downstream from the combustion chamber, keeping the dirty emissions blowing out of the tail pipe in check.”

      • I do not know the full mathematical gives and takes, but for internal combustion engines, the efficiency is affected by the difference in temperature of incoming and outgoing gases, more elegantly described by the Carnot Cycle.
        For general interest, from the Net,
        “If we see a heat balance sheet of the internal combustion engines for a spark ignition or gasoline engine we find that the brake load efficiency is between 21 to 28%, whereas loss to cooling water is between 12 to 27%, loss to exhaust is between 30 to 55 %, and loss due to incomplete combustion is between 0 to 45%.
        “Similarly when we analyze the heat balance sheet of a compression ignition or diesel engine we find that it has a brake load efficiency between 29 to 42 % and loss to cooling water is between 15 to 35 %, losses to exhaust is between 25 to 45 %, and losses due to incomplete combustion is 0 to 5 %.”
        Now auto engineers know these matters far better than you or I do, so they are well aware of the need to watch particulates, indeed any effluents that bureaucrats can write into a regulation that will cost them money. So I leave judgemental debates like the one here to the professionals.

      • Right on Commie, direct high pressure fuel injection into the cylinder WAS THE TRADITIONAL way of doing it eons ago.
        Port fuel injection was a lame el cheapo pressurized carburetor. You just blow metered gas into the port, instead of having intake manifold vacuum SUCK the gas out of the carburetor jets.

    • Question —
      Do diesel engines also use corn juice like gasoline engines? Until today I never knew I didn’t know that. Implications?
      Eugene WR Gallun

  8. “Auto industry experts predict that more than 50 percent of cars on the road by 2020 will …use a relatively new type of fuel-efficient engine.”
    Auto industry experts predict that more than 50 percent of cars on the road by 1957 will …use a relatively new type of turbine engine.
    Auto industry experts predict that more than 50 percent of cars on the road by 2015 will …use a relatively new type of battery powered engine.
    Auto industry experts predict that more than 50 percent of cars on the road by 2050 will …use a relatively new type of mind controlled engine by the google panopticon.
    Auto industry experts predict that more than 50 percent of cars on the road by 2075 will …use a relatively new type mortar to bond them to the road in the post apocalyptic dystopia.

      • Well, my 8 yr. old lap top suffered a fatal black screen. I have been spending more time with the Google Borg then I wanted and I have been assimilated to the tune of $800.00 dollars.

    • “Relatively new Bull Sh** ” is what it is.
      High pressure direct fuel injection into the cylinder like in a diesel was THE traditional way of doing fuel injection.
      Port injection, also known as a pressurized carburetor, is a cheap junk substitute for fuel injection into the cylinder, which is as old as the hills.

  9. With direct petrol injection, a two-stoke may be possible with a blower to clear the exhaust. And some better valve tech to breath easier:

    • I think you will find the Napier Deltic engine was a two stroke diesel, valve and camless, blown engine. Used in diesel electric locomotives in Britain in the 60’s. It was replaced because of emissions, sometimes called clag.

      • “I think you will find the Napier Deltic engine was a two stroke diesel, valve and camless, blown engine”
        It was indeed. 3 banks of cylinders arranged in a triangle, with a crankshaft at each corner. Originally designed for marine applications it found fame in the British Rail Class 55 “Deltic” locomotive, which had a pair of them (1650hp each). Even when operating with only one engine running it was still more powerful than most other locomotives of the day.
        There are still a few preserved examples “clagging” the countryside, to the delight of enthusiasts, and the horror of environmentalists!

        Most of that smoke is unburnt lubricating oil – the engines are very complex, and (I suspect) they are left well alone as long as they still run…

      • The Napier Deltic with its 18 cylinders and 36 pistons was a wonderfully compact, powerful engine, originally designed for marine applications. Its major disadvantage was great difficulty servicing due to inaccessibility.
        There was also the light, compact 3 cylinder Commer TS2 opposed piston supercharged diesel, popular in trucks in the 1950s and 1960s.

      • Napier Deltic was a copycat of the original two-stroke diesel engine, the Winton 201A. It powered the 112 mph speed record of the Pioneer Zephyr train in 1934

      • Newest US locos are “gensets” w/three 700 hp engines turning on/off as needed. Seem to be just switchers so far. Not a locomotive-design engineer, but seems overly complicated — why not just shut off some of the cylinders on a single engine instead?

    • Ulric, you are correct. The traditional two stroke engine was a Rube Goldberg Engine/Carburetor combination, which always resulted in the intake and exhaust ports (effectively) being open simultaneously, so a lot of fuel went straight out the exhaust.
      Going to (real) direct fuel injection allows you to supercharge the engine, even turbosupercharge, and wait until the cylinder is buttoned up tight, before you squirt in fuel and ignite it with a spark.
      A direct advantage of going two stroke, would be size and weight reduction.
      But a nice high tech fancy engine design project, if I was a new engineengineer.

      • A radial three cylinder is what I had on mind to keep the crankshaft short, with large inlet valves in the head, and outlet ports in the cylinder wall at the bottom of the stroke.

        • “with large inlet valves in the head, and outlet ports in the cylinder wall at the bottom of the stroke.”
          The six cylinder overhead cam Foden supercharged two stroke diesel worked the other way round, with the inlet through the ports at the bottom of the bore and exhaust through two valves in the cylinder head. Due to efficiency and blowdown the exhaust gases were so cool that the exhaust manifolds were aluminium castings, as were the cylinder block and head. A 4.5 litre Foden engine was capable of replacing a conventional Leyland or AEC engine of double or greater capacity and much more than twice the weight.
          If the silencers fell off, the noise was truly stunning!

      • “The six cylinder overhead cam Foden supercharged two stroke diesel worked the other way round, with the inlet through the ports at the bottom of the bore and exhaust through two valves in the cylinder head.”
        Wouldn’t that mean having to open the exhaust valve before the inlet was open? Yes fantastic sound, there are some clips on youtube.

    • ” the additional carbon can coat the intake valves that are no longer being cleaned by incoming fuel ” You’re getting this carbon from where ? The air ?
      Sorry , that statement does not make sense . Care to explain ?

      • This video explains standard 4 stoke engine operation.

        The difference with the new engine design is fuel is injected directly into the cylinder, not mixed with air and passed through the inlet valve.
        This results in less “washing” of the inlet valve ,which can cause carbon build up on the valve , and a poor seal during the compression stroke.
        This reduces power output from the engine.

      • Sigh…..the carbon has to come from oil leaking past the valvestem seals . On new engines this should be miniscule . So , why will this be a problem ? Poor design ? Poor QC ? Models say so ? I’m listening……

        • How about a more off the wall reason. The more efficient motor produces a larger fraction of CO2 and less CO and unburned hydrocarbons, which is what catalytic converters were primarily designed to eliminates from exhaust. The catalytic converter is still hot dealing with the NOx and perhaps even hotter since there are fewer water by-products from removing inefficient combustion products so perhaps some CO2 is being broken down into C and O2 by the converter.

      • And you will notice the animation is of a 16 valve engine, they are more efficient as they allow more air to pass through the induction system in to the cylinders. And a turbo, you get even better volumetric efficiency at higher revs.

  10. I suspect this is complete codswallop. I doubt that there is much room for particulate emissions by gasoline engines under current federal rules. I know I don’t see or smell much from late model gasoline engine vehicles.

  11. “their impact on the climate is uncertain”
    Wouldn’t most of it be in the bottom 30 cm. of the atmosphere anyway (unless your exhaust pipe points up like a Diesel)? You don’t have to stick many C atoms together to get a particle that will settle out of the atmosphere rather quickly, even when its a little windy.

  12. Can anyone answer the following questions?
    1) Why is it so difficult to filter black carbon from the exhaust of GDI engines?
    2) How long does the majority of black carbon remain airborne and how far does it travel when released near the ground?
    3) Less efficient engines require you to burn more fuel to go the same distance, which would release more CO2. So which is worse from a global warmer’s perspective, the increased CO2 emissions from less-efficient engines or the black carbon emissions from GDI engines?

    • Louis says: July 13, 2016 at 6:00 pm
      … Why is it so difficult to filter black carbon from the exhaust of GDI engines?

      It’s not difficult at all. The catalytic converter does a good job of getting rid of it.
      Walter Sobchak used the right word … codswallop. Yep, that expresses my feelings exactly.

      • The catalytic converter is designed to remove NOx, carbon monoxide, and gaseous hydrocarbons. It is not designed to remove particulate in gasoline exhaust.
        Gasoline particulate filters require some tailpipe redesign, can induce backpressure and add overall cost to vehicles, which is why auto makers are resistant.
        As for how long black carbon lasts in the atmosphere, it can be days to weeks, but in that time it can transport long distances. Evidence of black carbon from urban areas has been found in the Arctic, which can be especially bad since it changes the reflectivity of the snow surface.

      • Mark says: July 13, 2016 at 8:20 pm
        The catalytic converter … is not designed to remove particulate in gasoline exhaust.

        That’s mostly true. Most modern catalytic converters don’t run hot enough to oxidize the soot. I think some of the old ones did, but they would start a fire if you parked your car in the wrong place, like on dry grass or leaves for instance.
        Diesels, on the other hand, have a much bigger problem with soot. In that case, the catalytic converter captures the soot and then undergoes a periodic high temperature cycle to burn it off. link

  13. As a former mechanic who saw the transition from carburettors to electronic direct fuel injection, I view the assertion that the latter leaves more pure carbon (or soot which is what I think is meant by black carbon) with great some scepticism. (
    Electronic fuel injection has to be the greatest invention and asset to petrol using engines in the modern motor car.
    In the days of carburetted engines the spark plugs needed changing or cleaning evry 6000 miles or so. In those days the plugs were either sooted/carboned up and had become unserviceable for that reason by 6000 miles or they had run hot and the electrodes were burned which also rendered the plug unserviceable.
    Often a combination of both had contributed to the unserviceability of the plug.
    On my now elderly electronic fuel injected Subaru, the plugs have been changed twice and each time the plugs were like new. After the second time I ceased bothering about them and after nearly 10 years the engine still runs perfectly.
    Although these are platinum plugs, I know from my experience that these would have needed servicing at about 10,000 miles. I do about 12,000 miles per year.
    The reason for this performance is the precision of which the injectors feed the atomised fuel into the cylinder. This results in complete burning all the time and under all conditions.
    Plugs will be eroded by a lean mixture, carboned up by a rich mixture, but the injector gets it right every time.
    As one can see, it is extremely unlikely that a fuel injected car is going to emit black carbon or soot greater that the traditional carburetted vehicle if it emits any at all.and therefore I think the paper is based on some assumption that makes the whole paper meaningless.
    PS Actually I also majored in economics at university after I completed my mechanics apprenticeship.

    • … it is extremely unlikely that a fuel injected car is going to emit black carbon or soot greater that the traditional carburetted vehicle if it emits any at all.

      That’s true but in fairness I think they are comparing port injection with direct injection. In that regard, they are comparing darn little with not very much at all.
      In addition to injection and catalytic converters, I would also add electronic ignition. Modern cars are a marvel. 1960s Corvettes produced around 450 Hp, spewed pollution, and were a bit of a bear. Modern Corvettes produce 650 Hp, meet stringent pollution standards, and are quite responsive. Sadly, they are also completely absent from my driveway.
      I’m not sure if it is an urban myth but there was the story that if you parked a modern car behind a pollution spewing 1960s behemoth, the modern car’s exhaust would be cleaner that the air that it took in.

      • According to the manufactures training video I had to watch before I climbed into the 2015 Freightliner Cascadia I’m driving now, Detroit diesel claims the pollution control systems on the DD15 engine in that truck result in it’s exhaust being cleaner than the average air quality in highly congested areas in major cities.

  14. Gasoline direct injection engines are NOT new. Mercedes had them in their 300SKR in 1954.
    The car that Stirling Moss won the last Mille Miliga in 1957 was one of those. The engine is efficient because the fuel / air in the combustion chamber is very close to theoretical stochiometric. The compression ratio can be raised and thus the BMEP and power/displacement. Of course the early ones were not computer controlled and were mechanical in nature and thus quite expensive and finicky. They require nozzles much smaller than the current diesel injectors of yesteryear.

    • “Mercedes had them in their 300SKR in 1954.”
      Taken from the WWII Daimler-Benz aero engines that, unlike the Allied fighters, permitted the Me109s to pull negative G without the engine stopping or – in the worst case – catching fire, of course!

    • Three liter version of the 2.5 liter formula one GP engine in the W-196, with which Juan Manuel Fangio, and Sterling Moss cleaned up the GP events of 1954-55.
      As I recall, at Monza, for the Italian GP, the W-196 sported an enclosed wheels streamlined body, more like the 300 SLR sports car. The regular one was open wheel.
      Straight eight engine, with desmodromic valves (no valve springs)
      It was also a 300 SLR that went flying up into the stands at Le Mans and killed a whole bunch of people, including the French driver. If I’m not mistaken Peter Collins was the co-driver of that car, before it went flying.
      A W-196 recently sold for $29M, a world record price. But it was Fangio’s 1954 car to a total one of a kind.
      Blows my mind, that Mercedes, ever let a W-196 out of their sight, let alone hands.
      Rudolph Uhlenhaut, the chief Mercedes designer (I think) had his own personal 300SLR with the 300 SL gull wing coupe body.
      Dennis Jenkinson, wrote an uproariously funny article in Motor Sport magazine, about riding up to the Swedish Grande Prix with Rudolph from Stuttgart in his gull wing 300SLR, with the doors open doing 180 MPH along the Swedish country roads.
      Jenkinson drove back with a French GP chap, in a 2CV citroen.
      The W-196 / 300SLR had all wheel inboard disk brakes. Mercedes cast the engine blocks with NO water jackets on them, so they could polish the water channels smooth for better coolant flow, and then they welded on sheet plates to close everything up.
      Pretty fancy welding.

      • Correction, I think that was Auto-Sport magazine; the one with the BRG green on the cover

  15. Increased spark plug life is a function of better materials and capacitor discharge ignition systems.
    We are talking 60 – 80 KV instead of 8 – 10 KV for the Kettering versions.

  16. I drive a Chevy Volt, which is an amazing car. I usually describe it as a short range electric car, and long range hybrid. The all electric range is ~40 miles (less in winter, more in summer), and that is enough to cover the daily commute of most Americans. In hybrid modes, it is less efficient than a Prius, but so much more rewarding to drive. Overall, an 80% reduction in tailpipe emissions of passenger cars is certainly possible with today’s technology, let alone with improvements already in the pipeline (no pun intended). Electric cars are also a perfect fit for a renewable grid, since they can buffer variability. If anyone believes that electric cars will “tax the grid” and lead to blackouts, think again. Only modest grid improvements will be needed to accommodate increased demand.

    • I suspect a few million people all getting home after work and plugging into the grid almost simultaneously might need a bit more than “modest” improvements to the grid.

      • Felflames, short sighted reply. Electric cars will be ‘smart’. You would plug them in and they would figure out the best times to charge based on grid capacity, level-loading, etc. Like how Google tracks you. It would know your driving habits, length of commute, days of the week, estimated departure time, travel speed, GPS, etc. Possibly even tied to your phone. Unexpected emergency, there would be an override feature to quick charge. Although I do agree, the grid would need new investments (power and technology) to make it work.

      • Well Duncan, TESLA made a smart electric car, and it killed it’s non driving rider deader than a door nail, by driving full tilt into the side of a truck; which is “didn’t recognize”.
        So much for smart cars.
        But then only a total idiot would get into a car which is going to drive him somewhere, but is not on rails.
        What fool would not be paying attention to the roads, while his car is driving itself for him ??

      • “and it killed it’s non driving rider”
        The electric motor did not kill the driver, the self driving software did. I don’t know the circumstances around the accident. Technology can be great until it does not work. Elevators, airbags, planes, toasters, seat belts, electricity, medications, dams, etc have all killed people. No one would suggest we get rid if these modern conveniences. Many of these items have saved more than they have killed. I think you answered your own question, who would rely on the car to do all the driving, at least not yet.

    • Electric auto’s are the way of the future, regardless of how they are charged (coal, gas, nuclear, solar, etc). The inherent efficiency and configurable torque, speed and HP possibilities electric motors provide surpass a gas engine by far. For example, I can rotate a 700hp electric motor just by grabbing the shaft with one hand. Only two bearings provide resistance. Try that with a V8. They are more reliable, lighter and basically maintenance free. No transmission, no cooling/radiator, no drive train to worry about. Just waiting on the next leap in battery technology to hopefully provide quick charging, inexpensive, power dense and environmentally ‘clean’ materials. Something like a capacitor.

      • I was not suggesting cars need 700HP, although it would be nice. Through my work I order fractional into the hundreds of HP, multiple dozens a year. We size them and engineer them into systems. We test them in-house. Yes, I have a lot of respect for them. A non-optimized (off the shelf) 200hp motor is about the size of a 4-cylinder engine. The electric motor could make 200HP, everyday, all year and it would not blink. Design above the duty factor the same motor could make 300-400HP for short periods of time (acceleration). Heat becomes an issue though. They are so reliable motors can be in service for multiple decades, only requiring bearing replacement that only takes a few hours. After that, they can just be rewound.

        • A friend was in the Navy for some time in the ’70s, and his shipboard task was rewinding very large electric motor stators. He wore special gloves and his main task was to feel for what he called “fishhooks” or nicks in the copper wire as it slid through his hands at a fair clip, one of those monotonous jobs which would at intervals suddenly become rather frantic and not without peril.

  17. I’ll try again, but I couldn’t get past the word “Naomi” on the first pass. My hideousness meter is clearly working well, perhaps too well.

      • With the same transcription factors also inducing the elitist, fascist, hideous lying propagandist genes too – not that I’m saying this is true of this unfortunately named person, although I probably won’t read it anyway to find out.

  18. Doesn’t this study mean they have now decided reduced albedo due to particulate pollution was the cause of global warming rather than the “greenhouse effect” ?

    • Or is this in addition to the “greenhouse effect” so expanding the FF “problem”?

  19. Worked professionally on cars for several years and maintain my own. Seems to me a properly maintained and operated intake injected gasoline engine doesn’t produce black carbon. Raising the compression ratio would help, but that produces more NOx. BC is obviously a diesel problem. Another solution to an imaginary problem?

      • Does not look like a Mazda 13B (Single rotor) or 20B (Twin rotor) to me. But interesting none the less.

      • They turned the Wankel inside out. Wankel has a lozenge shaped cylinder and triangular piston, only fires on one side. This one fires on each corner, 18:1 compression ratio. 20 to 30% more fuel efficient min. 30% weight reduction over conventional engine with same output. They did a 4 pound motor with 3 hp output, replaced a 40 lb motor on a go kart and ran with it. They think they can improve it to 3 lb and 5 hp.

        • Sounds promising. Maybe it will be the exception to the usual fly in the ointment asterisk, which with the Wankel were the seals. What’s the maintenance schedule and TCO?

  20. All carbon is a pollutant, therefore we must ban carbon and all of its compounds. Sounds a bit silly but not much sillier than what Bill Clinton (mr Hillary) said about chlorine.

    • I just had an epiphany. Why not just paint the black carbon particles white as they’re exiting? A paint reservoir and a couple of spray nozzles …

  21. If you thought exploding air bags were a problem, then get ready for a rash of possible car fires from overheating particulate filters. In CA, which mandated them on all new diesel trucks, the trucking industry has experienced numerous fires and destroyed trucks. See
    And see for the obligatory burning truck photo.

  22. Here’s a potential Deus ex Machina that would be even more remarkable than Rossi’s e-cat “cold fusion” gadget: the Papp engine. It uses, supposedly, some sort of unknown nuclear reaction triggered by a spark in a sealed cylinder containing a mix of noble gases in a modified gasoline or diesel engine to provide 6000 hours of free 150 horsepower. The designer, Bob Rohner, a former assistant to Joseph Papp, wants beaucoup bux before revealing the secret. He & his deceased brother allegedly got it perfected and running in 2012. (An earlier version was supposedly debunked.)
    Here’s the link to the home page of his site — click on the tabs at the top for more. It’s worth it just for entertainment value, which I fear may be all it amounts to. Still, you never know . . . .
    See also:
    [Interview + very good article]

  23. We have to save the earth. We must build a new engine. We must build a new engine. We must build a new engine. Hold on. Black carbon?! Dear Zeus (coz God allegedly is a denier) we must burn the new enginre. We must burn the new engine. We must burn the new engine. Hold on what about the ice bergs? We must bury the new engine. We must bury the new engine. We must bury the new engine. Hold on..
    ..and thats why eco-nut bars should be treated like the father of the brides’ dance moves. With thinly veiled mockery, for as short a possible time so as to not cause a scene & packed away at speed.

  24. Call me a silly old green but making cars that last much longer (say twice the mileage) before having to be scrapped would reduce their carbon footprint per mile dramatically.

    • Nope. It is a numbers game. Have to make more to make more profits. Make more profits, make more, and so on…
      As we know does not always work out that way.

    • I oppose the “Green Agenda” and see it as anti-American, anti-progress, anti-human, anti-Christian and anti-justice but see no connection between how long vehicles last and being “green”. I bought new trucks in 1980, 1988, 2003 and 2013. Change the oil, drive thoughtfully and pay attention and things last.
      I use trucks for much over 100,000 US miles and trade them off because salt use in Rockford, Illinois is measured in rail-car loads
      Maybe Ford’s aluminum trucks will help but I have replaced brake lines, transmission coolant lines, fuel tank straps and on and on. Plastics seem attractive and fiber and resin stuff may work. Most “Greens” would hate materials progress of that kind.
      Longer lasting cars would be good particularly if China, India, Indonesia and a lot of other Nations reject socialist economics and let their people succeed. Selling to more customers, even if less often, helps the bottom line.
      A better engine may also be great progress but I too am suspicious of recycled ideas until I see something new in those ideas. Maybe this is a real improvement and maybe this is another “green” red herring. Or six day old carp.

  25. brians356 July 13, 2016 at 10:31 pm
    I see ambulance chaser ads on TV alleging talcum or “baby powder” causes cervical cancer. Why didn’t I think of that?
    There is a possible connection.
    Talcum powder is pulverised talc, a micaceous-clay mineral that is commonly found in rocks that contain white asbestos [chrysotile]. Poor quality talc could be contaminated with asbestos.
    However no one has been able to show a link between using talc and any form of cancer as yet.
    There’s money in it though. Johnson and Johnson have lost two cases where they have had to pay out $72 million and $55 million. I think they lost because they didn’t include warnings that stated that there was a faint risk that talcum powder could be, theoretically, weakly carcinogenic.
    So there is no evidence that talcum powder causes cancer but because J and J didn’t include a warning that the possibility was there [I suspect it’s less carcinogenic than eating toast] they got rolled.
    Nothing like the smell of money to get a lawyer’s pulse racing

    • So why would asbestos in talcum powder cause cervical cancer (per the TV ad), not lung cancer?

  26. “…more than 50 percent of cars on the road by 2020 will use a relatively new type of fuel-efficient engine.”
    Oh really? How do they figure that? In just four years? Bull. I also have serious doubts about the actual benefits of these engines. Will the fuel-savings outweigh the likely-increased cost of these engines? What about maintenance costs? Adding extra soot to the air we breathe doesn’t sound like such a good idea either. The real bull, and a giant red herring to boot is their obsession with its supposed impact on climate.
    I hope this study didn’t get printed out. That would be a big waste of paper. Think of the trees.

    • Stratified charge has been the dream of automotive engineers for many decades but is finally enabled in reliable and cost-effective form by the precise timing and metering of modern GDI.
      In a port-injected engine, a fuel-air mixture enters the cylinder and is compressed and then ignited. Some of the fuel is adjacent to the relatively cool metal envelope and in those locations the flame front may be quenched before combustion is complete or else much of the heat of combustion will be rapidly transferred to the nearby “cool” metal. Downstream, the catalytic converter handles any unburned fuel.
      In the ideal stratified engine the cylinder is filled with air only. At the right moment, fuel is injected into the center of this compressed air and the compact fuel-air ball is ignited. Combustion progresses outward until the fuel is depleted, before reaching the cool surrounding metal, and resulting heat expands the remaining air within the cylinder.
      In theory, stratified charge enabled by GDI results in more complete combustion and less wasted heat. But initial combustion within the fuel ball is typically fuel-rich which can lead to some byproducts which may require special downstream processing. Service experience also indicates that the injectors may be subject to carbon deposits which lead to inconsistent performance as mileage accumulates within large fleets subjected to various gasoline formulations.

    • Well people still rely on Wikipedia for their facts.
      Sure beats the ell out of me.

    • Just guessing … burning liquid fuel creates soot. Maybe in a gasoline direct injection some droplets don’t have time to evaporate completely. With a carburetor there is much more time to evaporate.

  27. Who cares about GW? Black carbon is harmful to health, carbon dioxide is not. Therefore preferring GDI engines to PFI ones is a crime against humanity. It is as simple as that.

  28. Well, really this is about all those pesky humans that think they get to live on the planet.

  29. “black carbon” the new scarecrow.
    Personally I prefer white carbon but I have a bit of a problem sourcing it.

  30. Thousands of vehicles in UK run with particulate filters illegally removed. MOT fails to catch filter removal because its body is welded and refitted back without the internal filter.

    • “Launch Price: £699.00”
      aka, scam
      “The box creates a small amount of very pure, very powerful hydrogen from our special water.”
      Oh, the water is ‘special’ so not a scam. [/sarc]

      • Kit
        Talk of different kinds of hydrogen and water I agree doesn’t help credibility. I suspect this was added by PR people. But cold fusion or homeopathy this is not.
        If history is any guide you will see the benefits of this technology when an American company markets it claiming to have invented it with the US patent mafia legal establishment on their side.

  31. “The graphs from PM2.5 studies are pretty interesting.”
    If you like absurd, unvalidated models. It is all part of the war on coal.
    There are no actual PM2.5 deaths in US cities. It is junk science. There are dose response curves for many things. For example, the L/D 50 for radiation is well established. 50% of the people exposed to that level will die from radiation poisoning. A direct cause that can be listed on a death certificate.
    The occupational exposure limit in the US is 5 rem/yr and no deaths are attributable. While some ‘claim there is no minimum safe level’, that theory is no more valid than the theory that low doses are beneficial.
    The claim of PM2.5 deaths is based on a statistical model linking emergency room visits and air pollution. Deaths only occurred in chronically ill patients over 75. What researchers mean by death is ‘premature death’.
    For example, my wife mother was rushed to the emergency room 5 times before she died. While recovering in a nursing home from hip surgery, she had a heart attack and did not have a pulse for 25 minutes. Four other times were for pneumonia.
    If she had been playing tennis or mowing the lawn maybe air pollution could be a factor. When I read the research and buried deep in the study is those dying were restricted to bed most of the time.
    When the cause of death is obvious, linking it with air quality statistics for 40 years ago is a little absurd.
    The EPA has one web site celebrating improved air quality and another discussing statistical ‘deaths’ to justify their existence.

      • The closest coal plant kills 8 a year according to one model. The model includes cities 250 miles away to get a larger population base. The model does not take into account geological features (aka, mountains). On a road map, rivers through these cities flows past the power plant. I understand how water changes direction flowing down hill. Wind is different. This is why I do not sail down Hell Canyon.

  32. “A study published in ACS’ journal Environmental Science & Technology has found that because the newer engines emit higher levels of the climate-warming pollutant black carbon than traditional engines, their impact on the climate is uncertain.”
    Well, I agree the impact is ‘uncertain’ but only because the core claim is rubbish. Black carbon in the exhaust is the result of incomplete combustion. Better combustion and high engine efficiency presupposes better combustion, not worse.
    Further, they are not really talking about BC they are talking about BC nanoparticles. Everyone knows that improving the combustion of fuels reduces PM2.5 – when detected by a light scattering instrument which can’t see anything below 0.1 microns. So it turns out the number (not mass) of BC nanoparticles increases as the total mass of PM2.5 is reduced by better combustion. This is the case with diesel engines, for example. Very clean when measured with one instrument, not so clean measured with another. The question is how do these particles influence anything?
    There is another core problem with the claim: BC nanoparticles do not interact with light which includes infrared radiation. That is why they are invisible to light scattering instruments. Infrared radiation is long wave light. Big BC particles do interact with light.
    Further, the way to deal with BC is to use a catalytic converter which burns them to CO2. I went through a stove factory here in North Carolina that uses catalytic converters in wood stoves to reduce the BC emissions. Cars already have them installed so I am wondering why the recommendation to install 80% efficient ‘filters’. You don’t filter BC, you reduce it to CO2.
    Even further, the way to deal with BC is not to generate them in the first place. BC particle are created by interrupting the combustion of carbonaceous fuel. Complete the combustion and presto. Then have a cat converter. Story complete.
    The paper and the alarmism it contains are a silly diversion. No one is going to take it seriously.
    There is an even further consideration with BC which is that it is an effective shading material that prevents light from reaching the ground, effectively re-radiating energy back into the sky as much as downwards. CO2 doesn’t do that, it allows the shortwave light in. BC doesn’t work like that. It shades coming and going, more effectively incoming than outgoing. Don’t believe everything you read, apparently.

  33. Retired auto research engineer with experience in this area but a person who doesn’t do well at writing.
    GDI results in a stratified charge of air and fuel. Gasoline combustion requires a homogeneous mixture of fuel and air at the correct portions of each. There is a range of portions of the two but it is not a wide range. The gasoline engine is a premixed combustion. The combustion begins at a point, the spark plug, and travels through the mixture. Basically when the portions are suitable for combustion the mixture is considered stoichiometric. The vaporized fuel and air must be well mixed.
    The diesel is different type of combustion. The combustion is a diffusion burn where the droplets burn as they vaporize after injection. The stoichiometry is correct at the interface between the vaporizing droplet and the surrounding air. Overall the mixture in the combustion chamber can be quite lean especially at low load.
    The two advantages of the diesel over the gasoline are increased compression ratio and there is no need for throttling. It is the lack of throttling on the GDI that gives the efficiency gain. The throttling losses that occur because of a need to deliver to the combustion chamber an overall homogeneous premixed charge of fuel and air as with port injection are eliminated. Throttling is a parasitic loss on the net work delivered by the engine. For instance, throttling losses are reduced in overdrive and an efficiency gain because the throttle is opened more than if not in overdrive and the difference between the pressure in the intake manifold and the exhaust manifold is reduced.
    With GDI stratified charge the overall stoichiometry in the combustion chamber can be quite lean especially at low load. Too lean for combustion. The ideal of GDI is to directly inject fuel into the combustion chamber and the fuel to vaporize and mix where an area of mixed fuel and air is homogeneous, stoichiometric and therefore suitable for combustion. This is difficult to do. The actual result is there are areas in the mixture that are too lean or rich for combustion. So there is some unburned or partially burned fuel leaving the combustion chamber resulting in an increase in some types of emissions.

    • My new Lexus RC-350 has both direct and port injection, solving the problem with the valves carboning up. This raises the cost of the engine a little, but prevents very expensive maintenance down the road. This one takes premium fuel to get full performance. It can run on 87 octane but the engine computer down-grades the spark timing to avoid pinging.

  34. “But cold fusion or homeopathy this is not.”
    Ptolemy2, it is still as a sc*m. Putting an expensive jug of water under the hood is a classic sc*m. A relative put one on my truck when I was in the navy. He was thinking that he could get a navy nuke to endorse it.
    One of the reason it is hard to spot a sc*m is that slick advertising is so prevalent. I thought hybrids were a great idea when they first came out. When I bought a new car in 2007, I did not buy a hybrid. Hauling around batteries is a bad idea because of the way people use hybrids.
    Green sc*ms are predicated on ‘feelings’ not life cycle analysis that show it is better for the environment.

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