Experimental Investigation of Performance, Combustion Efficiency and Emissions of SI Engine for Several Octane Numbers

Abstract

This research work gives a detailed study of the effect of engine speed, load, and octane number on performance and emission parameters on a four-cylinder four-stroke internal combustion spark ignition engine. Numerous tests were performed making use of a broad spectrum of engine speeds (800-3000 rpm), engine loads (0%, 25%, 50%, 75%), and octane numbers (80, 92, 95). The results revealed that higher RPMs and loads significantly enhance combustion power and thermal efficiency, while simultaneously reducing specific fuel consumption (BSFC) and carbon monoxide (CO) emission. As RPM was raised from 800 to 3000 under no-load conditions, the CO concentration was found to reduce by approximately 80%, while under full load conditions; it was even lesser. Furthermore, the study found that the emission of CO2 increases with engine speed and load about increased fuel combustion. For example, CO2 levels rose from 13% at 800 RPM to 15% at 3000 RPM, and when working in 75% loading. The study also pointed out that higher octane fuel assists in raising the combustion quality and lowering exhaust gas temperature especially when the load is high. This is well illustrated by a decrease in the exhaust gas temperature by approximately 100°C when the engine was operated with 95-octane fuel rather than 80-octane fuel under similar conditions. In addition, unburned hydrocarbon (UHC) emissions were significantly decreased with increased RPM reducing by 50 to 67% meaning that combustion at high speed was more efficient. Nitrogen oxide (NOx) emissions, however, increased with the Rpm and load, with an increase from 20 ppm of NOx at 800 Rpm to 150 ppm of NOx at 3000 Rpm because the rate of combustion is high at high engine speeds. These findings call for improved understanding and control of the operating conditions of engines and the quality of fuels available with a view to improving the overall performance of engines while reducing the rates of emissions. results also provide valuable insights that can inform the development of more efficient, environmentally friendly automotive engines and contribute to the formulation of policies aimed at reducing vehicular emissions.