TSCI with Wet Ethanol: an Investigation of the Effects of Injection Strategy on a Diesel Engine Architecture
To be published on April 2, 2019 by SAE International in United States
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 in particular uses “wet ethanol”, a mixture of 80% ethanol and 20% water by mass, to increase thermal stratification beyond what naturally occurs, via evaporative cooling. 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. Using a single injection at -350 deg aTDC was found to be the most effective way to introduce the 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), any increase in thermal stratification has time to mix out; however, the average in-cylinder temperature is decreased, delaying the 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 the 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.