Experimental Study of Ignition Delay, Combustion, and NO Emission Characteristics of Hydrogenated Vegetable Oil

In this article, a comparative study of hydrogenated vegetable oil (HVO) and diesel was performed in two constant volume combustion rigs and an optical accessible compression-ignited chamber (OACIC). Ignition, combustion, and nitric oxide (NO) emissions were studied under constant ambient gas density of 16.4 kg/m³, 21% vol oxygen concentration, and two different injection pressures of 800 and 1000 bar. Emission of NO was measured only in the OACIC, while a line-of-sight soot temperature distribution by applying two-color pyrometry was investigated in both setups. In general, the HVO as alternative fuel showed shorter ignition delay and less NO emission than diesel for both injection pressures. Due to difference in the molecular structure, soot temperature of biofuel flames had narrower temperature spectrum than conventional fuel. Moreover, this study reveals the significance of wall-jet interaction for utilization of the biofuel. The HVO was not found to bounce off the wall as conventional diesel, which led to relatively long flame residence time for the tested biofuel. Based on the revealed results, it is clear that a diesel engine operated on biodiesel will be characterized by lower NOx emissions comparatively to the one operated on conventional diesel fuel. This will ultimately lead to reduced energy consumption for exhaust gas aftertreatment in order to comply with environmental regulations. At the same time, the shift toward HVO, due to its both physical and thermodynamic properties, will require additional optimization of combustion chamber geometry and injection system and readjusting the injection strategies and timings.