Effect of Spark Timing on Performance and Emissions of a Small Spark Ignition Engine with Dual Ethanol Fuel Injection

Copyright © 2017 SAE International. Ethanol as a renewable fuel has been used widely in vehicles. Dual fuel injection is one of the new techniques in development for increasing the engine's thermal efficiency and reducing the pollutant emissions. This study reports experimental investigation to the dual ethanol fuel injection with a focus on the effect of spark timing on the engine performance at different volumetric ratios of ethanol directly injected to ethanol port injected. Experiments were conducted on a single cylinder 250cc spark ignition engine at two engine loads and 3500 RPM. The spark timing was varied from 15 to 42 CAD bTDC at the light load and from 15 to 32 CAD bTDC at the medium load, while the volumetric ratio of direct injection (DI%) was varied from 0% to 100%. Experimental results showed that DI100%, the best indicated mean effective pressure (IMEP) and thermal efficiency occurred at around 30 CAD bTDC at the light load and 23 CAD bTDC at the medium load, which were the minimum spark advance for the best torque (MBT). At MBT spark timing, the IMEP at DI56% and light engine load was 8.28% greater than that at 15 CAD bTDC which was the original spark timing set by the manufacturer, and the combustion duration (CA10-90%) was 41.8% shorter. These results were attributed to the improved combustion phase associated with the increased combustion pressure and temperature when the spark timing was advanced. However, the indicated specific hydrocarbon and carbon monoxide emissions increased with advanced spark timing and increased DI ratio. These could be caused by local rich mixture formed by fuel impinged to the chamber walls and the ethanol's cooling effect associated with the direct injection. On the other hand, because of the charge cooling effect of DI, the indicated specific nitric oxide emission decreased with increased DI ratio. At MBT timing and light load, the indicated specific nitric oxide emission decreased by 37.53% at DI56% and 67.39% at DI100% compared to port injection only