Experimental study on high fatty acid WCO biodiesel effects on RCCI engine performance, and emissions, considering fuel oxygen level

One of the significant challenges of RCCI engines is increasing the amount of UHC and combustion phasing control. On the other hand, a substantial challenge for biodiesel fuel is increasing NOx production. The low-temperature combustion (LTC) strategy is an effective method of reducing NOx. In this experimental study, an RCCI engine with diesel-gasoline dual fuel was experimentally evaluated under medium load conditions (BMEP = 20 bar) with a waste cooking oil (WCO) biodiesel mixture. The effect of changing WCO biodiesel fuel to diesel ratio (with different volume ratios of 0, 5, 10, and 20%) was investigated. The results showed that with a 5% increase in WCO fuel volume share, due to the higher cetane number of WCO fuel, the start of combustion (SOC) occurred about 4 crank angle degrees earlier. By increasing the volume ratio of biodiesel from 5 to 10% (B10), the amount of CO emissions suddenly increased by 33%; due to the increase in the viscosity of the high reactivity fuel (HRF), the fuel is not well atomized, causing poor cold combustion. In the case of using B20 fuel, the amount of unburned hydrocarbons (UHC) is greatly reduced due to the high pressure inside the cylinder.