Abstract
Amongst all low-temperature combustion (LTC) strategies, reactivity-controlled compression ignition (RCCI) combustion garners more debate from researchers because of its excellent combustion and performance characteristics and lower emissions over a wide operating range. In this experimental investigation, the consequences of the start of diesel injection (SoIdiesel) timing using different pilot injection techniques, such as single and double pilot injection (SPI and DPI, respectively), have been investigated. Tests were performed at a fixed engine speed and load (1500 rpm and 3 bar BMEP, respectively) using different premixed ratios (rp: 0, 0.25, 0.50, and 0.75) of methanol on an energy basis. Experimental results indicated that the start of combustion (SoC) and combustion phasing (CP) advanced with advancing SoIdiesel. However, too advanced and retarded SoIdiesel timings resulted in combustion noise and misfire. The use of pilot injection was found suitable for the RCCI mode, especially at lower rp. However, SPI and DPI strategies didn’t show significant variations in the combustion characteristics. Exhaust gas temperature (EGT) showed a random trend with SoIdiesel timing, and it decreased with the increasing number of pilot injections. RCCI mode produced higher hydrocarbon (HC) and carbon monoxide (CO) and lower oxides of nitrogen (NOx) emissions. All these gaseous emissions decreased with advancing the SoIdiesel. Particulate matter (PM) analysis showed that the RCCI mode emitted relatively lower PM than the baseline CI mode, further reducing with increased methanol fuelling. PM emissions also decreased by retarding SoIdiesel, in which reduction in smaller particles was dominant. The analysis of critical parameters such as brake thermal efficiency (BTE), HC, NOx, and PM emissions suggested that the optimum rp of methanol and suitable injection strategy can significantly improve the combustion, performance, and emissions characteristics of the RCCI mode.
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