This study investigates the effect of combustion phase (premixed and diffusion phases) duration on the emissions emitted from a high speed direct injection (HSDI) diesel engine fueled with neat (100%) rapeseed methyl ester (RME) and run at a constant speed (1500 rpm) with single injection strategy at constant fuel injection pressure (800 bar) and varying fuel injection timings (−12,−9,−6,−3,0) ATDC, for two loads (2.5 and 5 bars) BMEP. The obtained results were compared with those obtained when the engine run at the same conditions but with ultra-low sulfur diesel fuel (ULSD). In-cylinder pressure was measured and analyzed using (LABVIWE) program. calculation program specially written in (MATLAB) software was used to extract the apparent heat release rate, the ignition delay, combustion duration and specify the amount of heat released during the premixed and diffusion combustion phases (premixed burn fraction PMBF) and (diffusion burn fraction DBF). Emission measurements included; NOx, CO, THC, CO2 and smoke number (SN). The results showed that at high load, RME generate higher NOx, CO and THC. Measurements and calculations indicated that ignition delay of RME was shorter than that of ULSD, which means less PMBF. This conflicting effect is probably due to the advanced start of combustion (SOC) leading to higher combustion temperature inside the combustion chamber and there will be less time available to complete the combustion. The emission results at low load showed that NOx and CO, generated by RME were less than those generated by USLD. USLD produced soot more than RME at high load and less at low load.

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