Influence of methanol and diesel injection timings on the maximum methanol energy substitution ratio and performance of diesel/methanol dual-direct injection engine

An experimental study was carried out to investigate the impacts of methanol and diesel injection timings in a diesel/methanol dual-direct injection engine. By adjusting methanol injection timing, the maximum methanol energy substitution ratio can be increased to 96.0 %. Advancing the diesel injection timing increases the cylinder pressure and heat release rate, shortens the combustion duration, and controls the combustion cycle variation. Retarding the methanol injection timing and advancing the diesel injection timing enhance the indicated thermal efficiency. When the methanol injection timing is −60 °CA aTDC and the diesel main injection timing is −14 °CA aTDC, the maximum indicated thermal efficiency reaches 41.5 %. Furthermore, advancing the methanol injection timing and retarding the diesel injection timing affect emissions, BSNOx decreases while BSHC, BSCO, and BSsoot increase. When the methanol injection timing is −60 °CA aTDC and the diesel main injection timing is −14.0 °CA aTDC, BSNOx reaches its highest value of 3.1 g (kW h)−1, while BSHC, BSCO, and BSsoot all reach their lowest values, which are only 1.47 g (kW h)−1, 6.82 g (kW h)−1, and 0.06 g (kW h)−1, respectively. This article verifies the effectiveness of using dual-direct injection technology to achieve precise control of fuel concentration and reactivity gradient in the cylinder, which can provide a theoretical basis and data support for the design of diesel/methanol dual fuel engines.