Energy analysis during cold start and warm up period of a methanol engine hybrid power system under several novel energy conversion strategies

The use of methanol in engine hybrid power system has a wide range of potential applications, with the primary challenge being cold start issues. This paper innovatively proposes four strategies for starting and warming up the methanol engine, including motor dragging, motor dragging coupled with exhaust gas recirculation (EGR), motor dragging coupled with exhaust control, and motor dragging coupled with both EGR and exhaust control. These strategies can be implemented in methanol hybrid power system with minimal hardware modification costs, and not generate any emissions compared to traditional gasoline assisted strategy. The warm-up mechanisms of these strategies were analyzed and their effectiveness was verified by experiments. The optimum strategy, motor dragging coupling both EGR and exhaust control, has been demonstrated to enhance power input and improve the energy conversion efficiency substantially. Compared to the traditional gasoline assisted strategy, the energy consumption, energy conversion efficiency and the warm-up time in this strategy are 17.9 % lower, 5.1 % higher, 4.2 s shorter, respectively. These strategies well solve the problem of methanol engines being unable to start at low temperatures, which is expected to eliminate the cold start of the engine and directly enter the hot start.