Method and apparatus for controlling operation of a spark-ignition direct-injection engine

Abstract

Operation of a spark ignition, direct injection engine having an aftertreatment system including an oxidation catalyst and a selective catalyst reduction device is described. The method includes controlling to a stoichiometric air / fuel ratio and retarding spark ignition timing. Engine fueling is then controlled to a lean air / fuel ratio and spark is retarded. The engine is then operated to generate ammonia reductant. Engine operation then comprises operating at a preferred air / fuel ratio and controlling spark ignition timing to a preferred timing.

Description

technical field [0001] The present invention relates to the operation and control of internal combustion engines and exhaust aftertreatment systems, and more particularly, to engines operating lean of stoichiometry and associated exhaust aftertreatment systems. Background technique [0002] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. [0003] Engines configured for spark ignition may be adapted to operate in a stratified charge combustion mode under predetermined speed / load operating conditions. It is known that lean of stoichiometry operation using a stratified combustion charge may improve fuel economy but increase exhaust emissions, including nitrogen oxides (NOx). It is known to use an ammonia selective catalytic reduction device to reduce NOx in the presence of a reducing agent such as urea. It is well known that refilling the urea tank is a burden on the operator. [0004] K...

AI Technical Summary

Problems solved by technology

[0007] Known LNT devices absorb NOx emissions during lean burn operation of the engine and operate most efficiently in the temperature range of 250°C to 450°C, with reduced efficiency above or below this temperature range

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