Experimental investigation on the effect of in-cylinder heat release features on particle emissions characteristics of CNG–diesel RCCI engine

Abstract

In-cylinder heat release features and nanoparticle emissions have been investigated in this study for CNG–diesel reactivitycontrolled compression ignition (RCCI) engine. Study aims to determine the effect of low-temperature heat release (LTHR) and high-temperature heat release (HTHR) on the particles emissions from the RCCI engine. LTHR is obtained as a small peak (curve) before the main HTHR in the heat release rate curve. The LTHR and HTHR are not separated in heat release rate curve. The low-temperature heat release rate (LTHRR) is determined by extracting the heat release between start of combustion (SOC) to the intersection point of slope between LTHR and HTHR. The high-temperature heat release rate (HTHRR) is determined by fitting the trace between the intersection point of slope between LTHR and HTHR to the end of HTHR (the crank angle where the main HTHR turns negative after attaining the peak). This study calculates the amount of LTHR and HTHR by determining the absolute area under the LTHRR and HTHRR trajectories. Experiments are performed for different port-injected CNG masses (mc) and engine loads at a fixed engine speed of 1500 rpm. Single- and double-fuel injection strategy is used for injecting diesel. In the double-injection strategy, two cases are investigated. In the first case, diesel mass is split in the ratio of 50:50% between the first and second injection, whereas in the second case, diesel mass is divided into the proportion of 70:30%. CNG fuel mass, diesel start of injection (SOI), and the number of injections are controlled by engine electronic control unit (ECU). Results indicates that at a lower load with single-injection strategy, the lower amount of LTHR promotes the formation of small particles for 30° bTDC diesel SOI. It is found that increase in mc per cycle results in reduced and delayed LTHR and HTHR. With an increase in mc, the amount of LTHR decreases, and the total PN increases. The reduction in LTHR with an increase in mc leads to an increase in the formation of nucleation mode particles (NMPs) and a decrease in the accumulation mode particles (AMPs)