High-pressure direct injection of methanol and pilot diesel: A non-premixed dual-fuel engine concept

In order to reduce the climate impacts, methanol produced from carbon-neutral methods plays an important role. Due to its oxygen content and high latent heat, methanol combustion can achieve low soot and NO_x emissions. In the present study, direct injection (DI) of methanol is investigated in a non-premixed dual-fuel (DF) setup with diesel pilot. The present DF engine study is carried out via a specially-designed new cylinder head operating with a centrally located methanol injector and with an off-centered diesel pilot injector. The target is to inject methanol close to top dead center (TDC) in a similar fashion as in standard diesel combustion enabling robust operation with high efficiency. The ignition of the DI methanol is achieved with an almost simultaneously injected diesel pilot. The experiments were conducted in a single-cylinder heavy-duty research engine at a constant engine speed of 1500 rpm with a compression ratio of 16.5. The indicated mean effective pressure (IMEP) varied between 4.2 and 13.8 bar while the methanol substitution ratio was swept between 45 and 95%. In addition, the diesel pilot and methanol injection timings were varied for optimum efficiency and emissions. The introduced non-premixed DF concept using methanol as the main fuel showed robust ignition characteristics, stable combustion, and low CO and HC emissions. The results indicate that increasing both the load and the methanol substitution ratio can increase the thermal efficiency and the stability of combustion (lower COV) together with decreased CO and HC emissions.