Conventional and unconventional gas emissions and particle matter emissions of methanol CI engine with different EHN addition and compression ratios

Methanol, as a carbon-neutral resource, exhibits significant potential in the automotive sector, but its fuel characteristics are not easily compression ignited. In this experimental study, various strategies such as the preheating of the intake charge, augmentation of the compression ratio, and the introduction of 2-ethylhexyl nitrate (EHN) as an additive were implemented to enhance the combustion stability of pure methanol. In this study, an investigation was conducted on the combustion, fuel economy, and emission characteristics of pure methanol in a heavy-duty diesel engine. The experimental results revealed that the compression ratio of 21.5:1 had a more significant effect in reducing the ignition delay and combustion duration than the addition of 7 % EHN. Further, the compression ratio of 21.5:1 also improved brake thermal efficiency (BTE) by 4 %–11.9 %. In terms of emissions, with the addition of EHN in methanol under the lower compression ratio, NO and methanol emissions were higher. The peak particulate concentration and size of methanol gradually increased with load increasing. The incorporation of EHN resulted in an elevation in both the concentration and size, but still lower than those of diesel fuel. Based on the synergistic optimization of compression ratio and EHN addition ratio, the intake temperature required for achieving stable combustion was reduced, from 290 °C down to 70 °C, which was basically equivalent to 50 °C for diesel. The peak BTE of 30.19 % was achieved under the compression ratio of 21.5:1 and with the addition of 3 % EHN. This represented an 8.29 % improvement compared to the BTE of diesel fuel at the speed of 1144 rpm and the BMEP of 0.22 MPa. Thus, the pure methanol compression-ignition engine can reach the higher-efficiency, clean, and stable operation based on higher compression ratio (21.5:1) and low-ratio EHN addition (3 %), with a relatively normal intake temperature (70 °C).