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

Abstract

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.

Statistical analysis of ethanol/diesel dual-fuel combustion of compression ignition engines in RCCI mode using multi-injection strategies

“…Diesel, a highly reactive fuel, is sprayed directly into the cylinder at high pressure (70 MPa) as suggested in previous dual-fuel engine studies. 6,53 The basic features of ethanol and diesel are shown in Table 2.…”

“…The excellent fuel/air combination that results is not a favourable environment for the development of soot. 6 Furthermore, the addition of alcohol might reduce soot emission, 7 because of the high oxygen concentration of alcohols, which could increase the oxidation of soot particles and enhance combustion. LTC, on the other hand, is comparable to compression ignition (CI) in that both engines require auto-ignition to start.…”

“…Reactivity-controlled combustion includes multiple in-cylinder fuels with various auto-ignition properties in order to manage the charge reactivity gradient and consequently the charge stratified auto-ignition process. 1,6,53…”