TSCI with Wet Ethanol: An Investigation of the Effects of Injection Strategy on a Diesel Engine Architecture 2019-01-1146

Thermally Stratified Compressions Ignition (TSCI) is a new advanced, low temperature combustion concept that aims to control the thermal stratification in the cylinder in order to control the heat release process in a lean, compression-ignition combustion mode. This work uses “wet ethanol”, a mixture of 80% ethanol and 20% water by mass, to increase thermal stratification beyond what naturally occurs, via evaporative cooling of a split direct injection. TSCI with wet ethanol has previously shown the potential to increase the high-load limit when compared to HCCI. The experiments conducted in this paper aim to fundamentally understand the effect that injection strategy has on the heat release process in TSCI.

TSCI employs a split-injection strategy in which an injection during the intake stroke allows the majority of the fuel to premix with the air and an injection during the compression stroke introduces the desired level of thermal stratification to control the heat release rate. A single injection at -350 deg aTDC was found to be the most effective way to inject fuel during the intake stroke. The heat release process was found to be extremely sensitive to the injection timing during the compression stroke. At early injection timings (-150 to -100 deg aTDC), the increase in thermal stratification has time to mix out; however, the average in-cylinder temperature is decreased, delaying ignition. At late injections, such as -20 deg aTDC, there is not enough time for the spray to break-up and evaporate. Thus, combustion is similar to HCCI. Injection timings midway through the compression stroke (-90 to -30 deg aTDC) provide the ability to control thermal stratification prior to ignition in order to control the heat release process. Using multiple compression stroke injections allows the evaporative cooling of the spray to target more regions in the cylinder, improving combustion efficiency.