Potential of the reverse-reactivity controlled compression ignition (R-RCCI) combustion for maintaining ultra-low emissions and enhanced thermal efficiency

Abstract

Focusing on the reverse-reactivity controlled compression ignition (R-RCCI) concept, the intake and fuel supply parameters were optimized using a promoted genetic algorithm combined with the computational fluid dynamics simulation in this investigation. The combustion characteristics and energy utilization of both gasoline partially premixed combustion (PPC) and polyoxymethylene dimethyl ethers (PODEn)/gasoline R-RCCI were further evaluated in detail. The results indicated that R-RCCI exhibits superior performance compared with PPC. The optimized gross indicated thermal efficiency (ITE) of R-RCCI is 3.9% and 2.6% higher than that of PPC under 4 and 7 bar indicated mean effective pressures (IMEPs), respectively. The premixed high-reactivity PODEn in R-RCCI decreases the needed intake temperature, which provides more flexibility for the combustion phasing control. This correspondingly results in improved thermal efficiency for R-RCCI at 4 bar IMEP. Meanwhile, the lower intake temperature helps to decrease the heat transfer loss under 7 bar IMEP. Moreover, R-RCCI exhibits significant superiority over PPC on the unburned hydrocarbon (HC), carbon monoxide (CO), nitrogen oxides (NOx), and soot emissions under the operating conditions investigated in this work. For R-RCCI, the pre-combustion of PODEn can create a thermal atmosphere containing accumulated oxygen radicals, which provides the reaction conditions for the subsequent gasoline oxidation.