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.