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The size and distribution of a vehicle’s tailpipe particulate emissions can have a strong impact on human health, especially if the particles are small enough to enter the human respiratory system. Gasoline direct injection (GDI) has been adopted widely to meet stringent fuel economy and CO2 regulations across the globe for recent engine architectures. However, the introduction of GDI has led to challenges concerning the particulate matter (PM) and particle number (PN) emissions from such engines. This study aimed to compare the particulate emissions of three SI combustion strategies: conventional SI, conventional stoichiometric low-pressure exhaust gas recirculation (LP-EGR), and Dedicated-EGR (D-EGR) at four specific test conditions. It was shown that the engine-out PM/PN for both the EGR strategies was lower than the conventional SI combustion under normal operating conditions. The test conditions were chosen to represent the WLTC test conditions.

Stringent emissions regulations and the need for lower tailpipe emissions are pushing the development of low-carbon alternative fuels. H2 is a zero-carbon fuel that has the potential to lower CO2 emissions from internal combustion engines (ICEs) significantly. Moreover, this fuel can be readily implemented in ICEs with minor modifications. Batteries can be argued to be a good zero tailpipe emission solution for the light-duty sector; however, medium and heavy-duty sectors are also in need of rapid decarbonization. Current strategies for H2 ICEs include modification of the existing spark ignition (SI) engines to run on port fuel injection (PFI) systems with minimal changes from the current compressed natural gas (CNG) engines. This H2 ICE strategy is limited by knock and pre-ignition. One solution is to run very lean (lambda >2), but this results in excessive boosting requirements and may result in high NOx under transient conditions.