An Investigation Of High Load Reactivity Controlled Compression Ignition (RCCI) Combustion

Low Temperature Combustion (LTC) strategies are promising methods to achieve high efficiency and low NOx and soot emissions; however, they are typically confined to mid-load operating conditions due to challenges controlling the combustion characteristics. Reactivity Controlled Compression Ignition (RCCI) provides an additional measure of control, but efforts in expanding the operating range of this LTC strategy have been limited. The goal of the research presented in the following pages is to expand the operating range of RCCI combustion, particularly toward high load. To achieve this many variables were studied to quantify their contribution to load, as well as the repercussions they had on constraints. The constraints were typical of any engine operating strategy, including emissions, peak cylinder pressures, noise level, and stability. Stoichiometric RCCI was developed to achieve high load of 20 bar gross IMEP, but mixed mode combustion strategies proved to be the solution for expanding the operable range at this load. For optimization of mixed mode strategies, studies were done on the premixed fuel and near top dead center (TDC) fuel independently. For the premixed fuel, it was found that operation is primarily limited by noise and is very dependent on fuel reactivity. Fuel reactivity was found to be difficult to define but a more reactive fuel was not desirable for high load. The TDC fuel however, performed mostly independently of fuel reactivity and was limited by emissions constraints. Near TDC injections showed traditional soot vs. NOx tradeoffs that were controlled through mixing, but later injections proved soot production to be almost completely temperature dependent.