Quote:
Originally Posted by cRiPpLe_rOoStEr
An increase to NOx emissions is still often pointed out as easier to mitigate on a gasser fitted with direct injection than on a Diesel, yet the PM is a real PITA for both. OTOH a gaseous fuel injected at the vapour phase, such as natural gas, won't be so troublesome regarding PM.
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That's because the gasser can be run at a stoichiometric AFR and a still very homogenous charge. Yet direct injection with spark ignition lends itself to a lean burning engine with a stratified charge. But it seems most, if not all OEMs are going with the former and not the later in their direct injection engine designs.