Development of a Fuel Injection Strategy for Partially Premixed Compression Ignition Combustion

A production version of a V-8 engine was redesigned to run on partially premixed charge compression ignition (PCCI) combustion mode with conventional diesel fuel. The objective of the PCCI combustion experiments was to obtain low engine-out nitrogen oxide (NOx) and after-treatment tolerant soot emission level. Two fuel injection strategies were used during the PCCI combustion experiments: a) pilot-with-main injection strategy (Pil-M), b) pilot-with-main-and-post (PMP) injection strategy.

In the Pil-M injection strategy, a significant fraction of the fuel was delivered early during the compression stroke. The early pilot helped to prepare a lean-mixture of enhanced homogeneity before the combustion was initiated. The combustion of this pilot injection followed by the main combustion helped to reduce soot for a constant NOx value. The pilot-injection timing and quantity had to be selected appropriately to retain the fuel-efficiency. Such an injection strategy was successful up to an engine load-level of 10bar BMEP. At higher load levels, it was found that the Pil-M injection strategy was insufficient for a soot reduction. Therefore, the soot reduction was enhanced by using a small quantity of post injection to promote the late-cycle oxidation of soot. The PMP injection strategy helped to expand the load-limits of clean combustion to a load of 16.5 bar BMEP; however this injection strategy had a higher fuel-efficiency penalty as compared to the Pil-M injection strategy.