Advanced Low Temperature Combustion (ALTC): Diesel Engine Performance, Fuel Economy and Emissions 2008-01-0652
The objective of this work is to develop a strategy to reduce the penalties in the diesel engine performance, fuel economy and HC and CO emissions, associated with the operation in the low temperature combustion regime. Experiments were conducted on a research high speed, single cylinder, 4-valve, small-bore direct injection diesel engine equipped with a common rail injection system under simulated turbocharged conditions, at IMEP = 3 bar and engine speed = 1500 rpm. EGR rates were varied over a wide range to cover engine operation from the conventional to the LTC regime, up to the misfiring point. The injection pressure was varied from 600 bar to 1200 bar. Injection timing was adjusted to cover three different LPPCs (Location of the Peak rate of heat release due to the Premixed Combustion fraction) at 10.5° aTDC, 5 aTDC and 2 aTDC. The swirl ratio was varied from 1.44 to 7.12.
Four steps are taken to move from LTC to ALTC. The first is to advance LPPC, while keeping the other parameters constant. This was found to improve fuel economy and engine stability, but causes an increase in NOx. Since advancing LPPC allows the use of higher EGR rates, the second step is to increase EGR to reduce NOx, but this caused an incremental increase in soot emissions. To remedy this, the third step is to increase the injection pressure and/or swirl ratio. The fourth step is to optimize LPPC, injection pressure and swirl ratio. The effects of taking each of these steps on the combustion process and engine-out emissions are explained. Advancing the start of combustion and the associated strategy is referred to as (ALTC) that results in a more stable combustion process and engine operation, better fuel economy and reduced engine-out emissions.