Exploring the use of water injection to control the combustion and expand the operation load of an ethanol HCCI engine 2021-36-0053

Low Temperature Combustion (LTC) is an emerging technology that offers an alternative to conventional spark and compression ignition. A highly discussed LTC mode is homogeneous charge compression ignition (HCCI), which consists in a combustion of a highly diluted well-mixed charge at the end of compression stroke, when the charge reaches the auto-ignition state. Since HCCI is an LTC mode, it can result in low NOX emissions with an indicated efficiency comparable to a diesel engine. Otherwise, there are some challenges to overcome such as achieving high loads without knocking and combustion timing control. Several methods to control the combustion had been investigated, between them, the injection of water may be useful to extend HCCI knock free operation and to enable combustion phasing control. This work investigated the influence of water injection in the intake of an ethanol HCCI cylinder from a converted diesel generator set. The EGR, used in HCCI, was obtained via total recirculation of exhaust gas from a diesel cylinder. The results indicated that the combustion without water injection tended to start considerably before TDC with a very fast combustion and abrupt heat release rates causing knock. As consequence, the ringing intensity values were higher than the acceptable and the operational load was limited. It has been found that the water injection in the HCCI combustion retarded the combustion and increased its duration, preventing knock. The highest indicated mean effective pressure (IMEP) achieved was of 6.0 bar with a ringing intensity around 5.5 MW/m² with indicated efficiency of about 40%. Finally, the water injection proved to be an efficient strategy to control the combustion timing and to expand the operation range by controlling mixture's reactivity and intake temperature.