Effect of Different Fluids on Injection Strategies to Suppress Pre-Ignition

Pre-ignition is an abnormal engine combustion phenomenon where the inducted fuel-air charge ignites before the spark ignition. This premature combustion phenomenon often leads to heavy knocking events. The mixture preparation plays a critical role in pre-ignition tendency for a given load. Literature shows efforts made towards improving pre-ignition-limited-IMEP by splitting the injection pulse into multiple pulses. In this study, two direct injectors are used in a single cylinder research engine. A centrally mounted direct injector was used to inject Coryton Gasoline (RON 95) fuel early in the intake stroke. A second fluid was injected late in the compression stroke to suppress pre-ignition. The fluids used in the second direct injector was varied to see the effects of the molecule and its physical and chemical property on pre-ignition suppression tendency. Methanol, ethanol, water, and gasoline were tested as second fluid. Engine tests were conducted at 2000 rpm and at an intake pressure of 2.1 bar (abs). Although alcohols show high pre-ignition tendency as fuels, they were most effective at pre-ignition suppression when injected later in the compression stroke. The pre-ignition suppression led to a decrease in IMEP and an increase in cycle-to-cycle variation. Water injection was highly effective at maintaining peak IMEP values. Water injection was further explored for pre-ignition suppression. The water injection helped reduce pre-ignition count when injected at two different injection times each in intake, compression and late exhaust stroke.