The Load Limits of Low Temperature Premixed Compression Ignition Diesel Combustion

摘要

Simultaneous reductions in oxides of nitrogen (NOX) and particulate matter (PM) emissions from a light-duty diesel engine can be realized with implementation of low temperature premixed compression ignition (PCI) combustion. While very successful at medium-load conditions, PCI combustion is not yet suitable to cover the entire operational range of an engine duty cycle; excessive combustion noise, combustion instability, PM, carbon monoxide (CO), and hydrocarbon (HC) emissions confine the practical implementation of PCI combustion strategies within the operational regime. Using a light-duty production diesel engine, this work investigates the limiting factor(s) of full implementation of PCI combustion over the entire operational regime. It is found that PCI combustion is an excellent technique to reduce NOX and soot in the low to medium load range at a modest fuel economy penalty compared to conventional diesel combustion strategies. At very light loads, soot emissions are completely eliminated, but strategies that aim to eliminate NOX emissions at very low loads result in markedly high CO and HC emissions. This is especially bothersome because exhaust temperatures are low at these low load conditions, which tend to deactivate diesel oxidation catalysts (DOC). At high loads, PCI combustion becomes difficult to attain as soot emissions and fuel consumption increase rapidly. NOX, however, can be controlled very effectively. CO and HC emissions increase compared to conventional diesel combustion strategies. High exhaust gas temperatures, however, ensure sufficient DOC activity. While the trends shown in this paper are influenced by hardware and the engine platform, the overall characteristics of PCI combustion are thought to be valid for many diesel engine applications.