Influence of Fuel Injection Pressure on Gasoline/Waste Oil Biodiesel–diesel Blend (B20) RCCI Combustion: An Experimental Study

Waste oil-derived biodiesel is a promising renewable fuel for advanced combustion concepts such as Reactivity Controlled Compression Ignition (RCCI). However, the influence of fuel injection pressure (FIP) on gasoline/biodiesel RCCI combustion has received limited experimental attention. In this study, the effect of FIP was experimentally investigated using a diesel–waste cooking oil biodiesel blend (B20) as the high-reactivity fuel and gasoline as the low-reactivity fuel. Experiments were conducted at 1050 rpm with a premixed fuel ratio of 27%, over FIPs ranging from 150 to 350 bar and at two start-of-injection (SOI) timings of 25° and 40° bTDC. The study highlights that the response of different engine characteristics to variations in FIP depends on SOI for some parameters, whereas others are largely insensitive to SOI. Engine performance, combustion characteristics, and exhaust emissions were evaluated. The results showed that increasing FIP over a relatively large range increased brake power by up to approximately 2.4 times the minimum value, whereas the in-cylinder pressure peak did not follow the same trend. In addition, among the FIPs associated with relatively high brake power, an FIP was identified that resulted in lower NOx emissions at both SOIs while providing the highest brake power at one SOI. These findings demonstrate the importance of considering both FIP and SOI when selecting injection conditions for gasoline/B20 RCCI combustion.