Experimental Investigation on Reactivity-Controlled Compression Ignition Combustion Using Simple and Similar Molecular Fuels—Methanol and Dimethyl Ether

The effects of simple and similar molecular structure fuels like methanol (M) and dimethyl ether (DME) on the reactivity-controlled compression ignition (RCCI) combustion, performance, and emissions were investigated on a three-cylinder turbocharged manifold port fuel injection (MPFI) and common rail direct injection (CRDI) dual-fuel engine at different loads. Methanol-to-DME energy ratio (0% to 90%) and DME direct injection (DI) timing were optimized for better brake thermal efficiency and lower engine-out emissions. The higher cetane number and higher volatility characteristics of DME enhance the global reactivity gradient and fuel reactivity stratification compared to diesel (D). The viscosity, density, and lubricity properties of DME are different compared to D; consequently, DME fuel requires a dedicated fuel supply system. Hence, in the present investigation, the DME fuel supply system was designed carefully and integrated with the engine. The experimental results indicated that the rate of pressure rise (RoPR) is reduced by 1.1 bar/°CA, indicated thermal efficiency (ITE) and combustion efficiency increased to the maximum of 51% and 96.4%, respectively, at high load in M/DME RCCI combustion compared to M/D. Compared to M/D operation, M/DME operation decreased the soot emissions by 76% and increased the nitric oxide (NO) by 20%; whereas compared to conventional D operation, the reduction in NO and soot in M/DME operation is 80% and 90%, respectively. The reductions in the RoPR and NO are achieved without exhaust gas recirculation (EGR) in M/DME operation, and hence, EGR may extend the load range of RCCI combustion with lower NO emissions.