Strategies to Reduce Higher Unburned Hydrocarbon and Carbon Monoxide Emissions in Reactivity Controlled Compression Ignition

Abstract

<div class="section abstract"><div class="htmlview paragraph">Reactivity Controlled Compression Ignition (RCCI) is a promising, high-efficiency, clean combustion mode for diesel engines. One of the significant limitations of RCCI is its higher unburned hydrocarbon (HC) and carbon monoxide (CO) emissions compared to conventional diesel combustion. After-treatment control of HC and CO emissions is difficult to achieve in RCCI because of lower exhaust gas temperatures associated with the low-temperature combustion (LTC) mode of operation<b>.</b> The present study involves combined experimental and computational fluid dynamic (CFD) investigations to develop the most effective HC and CO control strategy for RCCI. A production light-duty diesel engine is modified to run in RCCI mode by introducing electronic port fuel injection with the replacement of mechanical injectors by the CRDI system. Experimental data were obtained using diesel as HRF (High reactive fuel) and gasoline as LRF (low reactive fuel). The combustion simulation was performed using the CONVERGE 3D CFD tool. A reduced PRF mechanism was used where iso-octane represents gasoline and n-heptane as diesel. After validation of engine combustion, performance, and emission parameters, parametric investigations were carried out to investigate the effects of HRF's start of injection timing, premixed energy share, and intake charge temperature on combustion and exhaust emissions. The results obtained from both CFD and experiment show that the start of injection and intake charge temperature significantly influence combustion phasing, while the premixed ratio controls mixture reactivity and combustion quality. The blending ratio of high HRF to LRF governs reactivity stratification, which controls the magnitude of low and high-temperature heat release, combustion phasing and combustion duration. Controlling the amount of LRF and HRF in direct injection (DI) allows for shifting the heat release rate, which modifies combustion phasing and rate of pressure rise. Multiple injection strategies using double pulse helped reduce CO formation and achieve better control over combustion parameters with improved efficiency. By varying IVC temperature, optimizing SOI timing using a double injection strategy up to 18.57%, 25.5% reduction in CO and 93.68% drop in HC emissions, 3.7% reduction in soot are obtained in RCCI compared to the baseline case.</div></div>