Experimental Investigation of Cycle-by-Cycle Variations in CAI/HCCI Combustion of Gasoline and Methanol Fuelled Engine

The development of vehicles continues to be determined by increasingly stringent emissions standards including CO2 emissions and fuel consumption. To fulfill the simultaneous emission requirements for near zero pollutant and low CO2 levels, which are the challenges of future powertrains, many research studies are currently being carried out world over on new engine combustion process, such as Controlled Auto Ignition (CAI) for gasoline engines and Homogeneous Charge Compression Ignition (HCCI) for diesel engines. In HCCI combustion engine, ignition timing and combustion rates are dominated by physical and chemical properties of fuel/air/residual gas mixtures, boundary conditions including ambient temperature, pressure, and humidity and engine operating conditions such as load, speed etc. Because of large variability of these factors, wide cycle-to-cycle variations are observed in HCCI combustion engines, similarly small variations in ignition timing and combustion rates result in wide variation in engine performance and emissions. Also, cycle-to-cycle combustion variations result in objectionable engine noise and vibrations. As a result of wide cycle-to-cycle variations, HCCI combustion can be achieved in an engine for narrow range of lean and rich operating limits. This motivates the researchers to systematically investigate mechanism and control of cycle-to-cycle variations on HCCI engines.