Experimental Study On HCCI Engine With DME/Methanol Dual Fuel

Energy lacking and environment pollution are two problems that all countries in the world are confronted with today. Homogenous Charge Compression Ignition (HCCI) combustion technology is receiving increased attention for its ultra-low NOx and PM emissions and high thermal efficiency. HCCI combustion process is hard to control because it is dominated by chemical kinetics of fuel air mixture. In addition, the HCCI operating range is narrow.A new method to control HCCI combustion process and to extend the HCCI operating range by using dual fuel (dimethyl ether / methanol) and cooled EGR has been proposed.A series of experiment are carried out on a single cylinder engine. The fuels are supplied by an electric controlled port injection system. The experimental results show that, the HCCI combustion of DME presents remarkable character of two-stage combustion process, but the DME HCCI operating range is narrow. By regulating the concentrations of DME and methanol, the HCCI operating range can be largely extended, and the indicated mean effective pressure (IMEP) reaches 0.77 MPa. The ignition timing advances and combustion duration reduces with increased DME supply. And with increased methanol concentration, the ignition timing delays and combustion is slowed down. Moreover, Methanol influences low temperature reaction greatly, low temperature heat release of DME obviously decreases in the HCCI combustion of DME/methanol dual fuel. Under normal HCCI combustion, less methanol (or more DME) should be applied to get high efficiency. For light load, low thermal efficiency results from DME/methanol dual fuel, So pure DME with high EGR rate may be a good choice for HCCI operation. While cooled EGR is used, with theincreased EGR rate, the ignition timing postpones, the combustion duration extends and the thermal efficiency increases. However, the maximum load of HCCI engine with DME/methanol dual fuel is little extended. The NOx emission of HCCI engine keeps at a low level at all operating points, but HC and CO emissions are much higher than that of traditional diesel engines. With increased DME, HC and CO emissions decrease, while with increased methanol, HC and CO emissions increase.The experimental results show that, employing DME/methanol dual fuel is an effective measure to control HCCI combustion. EGR is a method to control HCCI combustion as well. The paper's study is valuable to develop HCCI engine and achieve efficient and clean combustion of methanol fuel in future.