Soot Emissions from Gasoline Direct Injection (GDI) Engines

It was repoted that automakers had introduced several highpowered GDI engines at the Autoshow in Detroit this past week. Green Car Congress, a reputed place to learn about innovations and news of the auto industry had the following to say:

GM, Porsche and BMW are among the automakers announcing gasoline direct injection (GDI) engines in new models introduced at the North American International Auto Show in Detroit. Gasoline direct injection technology offers improved combustion and fuel efficiency, offering automakers either a way to deliver comparable power with lower fuel consumption, or increased power with less of a fuel consumption penalty.

Direct injection delivers precisely metered and timed fuel directly to the combustion chamber, enabling a more precise mixture formation. This also has a cooling effect in the chamber, enabling a higher compression ratio, and improving engine efficiency. Less fuel is required to produce the equivalent horsepower of a conventional port injection combustion system.

But somehow there is no discussion of the PM (soot) emissions from GDI engines??? Because the combustion process is a hybrid of the gasoline spark ignition and the diesel compression engine, there is a natural increase in soot emissions from a GDi engine (see here and here, for example). This similarity is more easily identified when particule number concentration is measured (instead of particulate mass). The increased PM emissions have been documented well in several studies in europe, and in fact, the Euro 6 emission regulations are expected to require GDI to meet the same PM/NOx criteria as the diesel engines in europe. While in the short term this may be possible using engine control technologies, and operating in certain regions of the engine map, this may not be possible for a long time. Under transient conditions GDi engines produce about as much soot as a modern diesel engine, and hence to reach PM regulatory limits, a particulate filter may be required.

Well, if a filter, and not just a typical 3-way catalytic converter is required on the GDi engines to reach the low particulate emission limits, it will be another wonderful growth opportunity for the filter makers (such as GEO2) especially in the US light duty market. We will watch and see. Both GDI and diesel engines provide a 20-30% improvement in fuel economy, which I am happy to endorse as long as the best available technologies, such as advanced ceramic particulate filters, are deployed to effectively remove the toxic emissions.


16 Responses to Soot Emissions from Gasoline Direct Injection (GDI) Engines

  1. Hi,

    Very interesting, I had no idea that a hybrid (spark vs. compression) was even being developed.

    I am told that NOx and PM are the primary problems with diesel engines. I have told friends that, despite these problems, diesel technology is less destructive to the environment because it is considerably more efficient. I speculate that if every single internal combustion engine in America were to suddenly become a diesel, we would immediately reduce our fossil fuel oil consumption by about 25%.

    Which engine technology is better for the environment?

    Do diesel engines emit more NOx and PM than a gas engine?


  2. Bilal Zuberi says:

    Hi Erik,
    Diesel engines do emit more PM and NOx. Because of low combustion temperatures, there is more nucleation of soot particles. NOx is generated because during combustion, there is excess N2 gas available inside the combustion chamber which splits apart tohelp make NOx.
    The new exhaust emission systems now available for diesel (such as SCR and diesel particulate filters) remove >95% of all particulate matter (soot), and >90% of NOx from the exhaust plumes. Hence, diesel engines are able to run as clean as gasoline engines. Infact, the Tier II Bin 5 categorization of diesel engines requires the diesel engines to be as clean as gasoline. Going forward, frankly, without additional emission control systems on gasoline engines, they can be more polluting than diesle engines.
    That said, you are absolutely right that if alll gasoline engines switched to diesel engines, and nothing else was changed, we would get a 25-30% fuel efficiency. That means millions of barrel of oil per month. Diesel is the most easily available technology to improve fuel efficiency in the mobile sector today.

  3. Rachna Patel says:

    What kind of mixture of fuel does diesel engines run on? say for instance ‘lean-burn’ engines use a ‘oxygen rich fuel mixture’ and conventional engines use a ‘rich mixture’ which contains more fuel.

    Also why do diesel engines produce more soot?
    Many Thanks

  4. Bilal Zuberi says:

    Hi Rachna, Diesel fuel runs lean whichis why it gets better fuel economy and lower CO and unburnt HC pollution.
    Diesel engines produce more soot because the engine runs at lower combustion temperatures. Under those conditions uncombusted hydrocarbons can coagulate and form soot.

  5. HelloWorld says:

    Peace people

    We love you

  6. Austin says:

    Thank you for a very informative article.

    In Norway, we’ve experienced a transition to more CO2-friendly car taxes. This favoured diesel-engined cars, and we saw a rise from 30-40 % diesel-powered cars, to a 80-90 % of the total market overnight.

    A few, but unfortunately very few, complained that this will very much increase local pollution from micro particles. Astma and allergic suffering will increase as a result from this.

    Now we see the same thing happening with GDI, and I have so far not found much protesting except from this website.

    How can we sacrifice our close enviroment just to gain a minor reduction in CO2-emissions? This is just another example of how CO2-emissions has been favourized on behalf of “regualar” pollution.

  7. polnajung25 says:

    This is the good articles about automotive. I will bookmark this articles. Thank you.

  8. Kasey says:

    Love the blog, thanks for the info. What do you think about GDI?? I signed up at ExplorePro.comThanks!@

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