On improving the controllability of low-temperature combustion by building two-stage sequential high-temperature reactions in an ethanol/diesel dual-fuel engine using multiple injections

Low-temperature combustion (LTC) has advantages in reducing emissions and improving efficiency, at the expense of hard controllability. To improve its controllability, this paper proposes a two-stage stratified compression ignition (TSCI) strategy, which aims to decouple ignition and the following combustion as two-stage sequential high-temperature reactions, and couple them to external events like multiple injections, supercharge, etc. A trace amount of high reactivity fuel (HRF) is injected near the top dead center (TDC) and auto-ignited, initiating the combustion process, which controls ignition. The highly premixed charge (HPC), whose equivalent ratio, temperature, reactivity can be tuned as needed, control the combustion course after ignition. Based on the TSCI concept, one demonstrative multiple-injection strategy is suggested and tested on a single-cylinder ethanol/diesel dual-fuel engine. It is concluded from the experimental results that the TSCI combustion process presents two-stage sequential high-temperature reactions, which is different from any other LTC strategies. This sequential combustion shows good controllability. Within a certain range, the ignition phase is directly and linearly related to the ignition-oriented injection (IOI) event. With the advance of IOI timing, the ignition is advanced consequently. Increasing IOI quantity has the same tendency. As for HPC, when HPC reactivity is increased, the maximum pressure raising rate (MPRR) is increased and the whole combustion process is more concentrated.