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As an alternative fuel, renewable diesel (RD) could improve the performance of conventional internal combustion engines (ICE) because of its difference in fuel properties. With almost no aromatic content in the fuel, RD produces less soot emissions than diesel. The higher cetane number (CN) of RD also promotes ignition of the fuel, which is critical, especially under low load, and low reactivity conditions. This study tested RD fuel in a heavy-duty single-cylinder engine (SCE) under compression-ignition (CI) operation. Test condition includes low and high load points with change in exhaust gas recirculation (EGR) and start of injection (SOI). Measurements and analysis are provided to study combustion and emissions, including particulate matters (PM) mass and particle number (PN). It was found that while the combustion of RD and diesel are very similar, PM and PN emissions of RD were reduced substantially compared to diesel.

Dual fuel engines have shown significant potential as high efficiency powerplants. In one example, SwRI® has run a high EGR, dual-fuel engine using gasoline as the main fuel and diesel as the ignition source, achieving high thermal efficiencies with near zero NOx and smoke emissions. However, assuming a tank size that could be reasonably packaged, the diesel fuel tank would need to be refilled often due to the relatively high fraction of diesel required. To reduce the refill interval, SwRI investigated various alternative fluids as potential ignition sources. The fluids included: Ultra Low Sulfur Diesel (ULSD), Biodiesel, NORPAR (a commercially available mixture of normal paraffins: n-pentadecane (normal C15H32), and n-hexadecane (normal C16H34)) and ashless lubrication oil. Lubrication oil was considered due to its high cetane number (CN) and high viscosity, hence high ignitability.

The performance and efficiency of spark ignited gasoline engines is often limited by end-gas knock. In particular, when operating the engine at high loads, combustion phasing is retarded to prevent knock, resulting in a significant reduction of engine efficiency. Since the invention of the spark ignition (SI) engine, much work has been devoted to improve and regulate fuel characteristics, such as octane number, to suppress engine knock. The auto-ignition tendency of the engine lubricant however, as described by cetane number (CN), has received little attention, as it has been assumed that engine lubricant effects on knock are insignificant, primarily due to low levels of average oil consumption. However, with modern SI engines being developed to operate at higher loads and closer to knock limits, the reactivity of engine lubricants can impact the knock behavior.