Annex A3 –Particle Emissions from Current Technology Engines

above very conveniently compresses a very large body of PM test data into two highly
informative charts. It can be readily seen that the relative emission rates of particles for each fuel type are similar in both the idle testing and the 50 km/h tests, even though the absolute values differed quite substantially.
Conventional diesels (those without any exhaust after-treatment to reduce particle levels) clearly have the highest emission levels while conventional multipoint injected gasoline and LP Gas fuelled vehicles are substantially lower. Readers should note that the vertical scale is logarithmic so each vertical division represents a ten-fold increase in particle concentration.
In both the idle and the 50 km/h tests, the conventional diesel engines have particle concentrations between 100 and 1000 times higher than most of the gasoline and LP Gas vehicles.
But it is interesting to note that direct injection gasoline (DIG) engines also have extremely high PM emissions – typically between 10 and 100 times higher than the current mainstream LP Gas and gasoline engines. The use of gasoline DI technology is likely to increase, as vehicle manufacturers strive to further improve fuel economy. But the charts tell us that this strategy has potentially serious environmental downside, given that gasoline PM emissions have not previously been considered sufficiently high to warrant regulation. The Ricardo results are consistent with the results of other studies into particle emissions from DIG engines.
Responding to the results of this research, the 2009 Euro 5 emission regulations introduce, for the first time, gasoline PM emission limits. This extension to the scope of Euro regulations specifically addressed gasoline DIG engines only – PM from gasoline engines with non-DI fuel delivery systems will not be regulated.
On a more general front, in the US there is a growing concern that particle emissions from gasoline vehicles may represent a larger health threat than previously understood. In 2006 the US Environmental Protection Agency (US EPA) released the results of a large scale testing program in Kansas City to measure particle emissions from gasoline fuelled cars and light trucks in various age groups. The results of these tests are summarised in Figure 9.2 below.

By way of comparison, the PM emission limit for diesel cars and light commercial vehicles in the Euro 4 standard (in force since 2005 in Europe and progressively adopted in many other economies) is 25 mg per kilometre (equivalent to 40 mg per mile). The 2009 (Euro 5) regulation reduces the limit to 5mg/km (8mg/mile).
From the above chart it can be inferred that many in-use gasoline vehicles are emitting significantly higher PM emissions than current technology diesels.
The high volatility of LP Gas results in almost instant transformation into the gaseous phase when injected directly into the cylinder. This greatly reduces the likelihood of direct injection LP Gas engines producing the high PM levels generated by their gasoline counterparts.