Theoretical Analysis of Performance Characteristics of Non- road Spark Ignition Engines

Non-road spark ignition (SI) engines play a critical role in Nigeria, particularly in agriculture, construction, and small-scale power generation. Despite their extensive use, there is limited research on how Nigeria's unique environmental and operational conditions such as high ambient temperatures, poor fuel quality, and irregular maintenance practices affect the performance of these engines. This study presents a theoretical analysis of the performance characteristics of non-road SI engines under Nigerian conditions, focusing on fuel efficiency, power output, thermal efficiency, and emissions. The effect of engine speed, engine load and equivalence ratio on the performance characteristics of non-road spark ignition engines were studied in this research. Three operating parameters (engine load, engine speed, and equivalence ratio) and eight engine performance parameters which are Brake Specific Fuel Consumption (BSFC), Brake Power (BP), Thermal Efficiency (TE), Brake Mean Effective Pressure, Exhaust Gas Temperature (EGT), carbon monoxide emission, hydrocarbon emission, and nitrogen oxide were considered in this work. Theoretical analysis was performed using a two-zone SI engine model, the resulting equations were solved with the aid of a computer program developed by the authors and implemented in MATLAB software. The effect of the operating parameters on the performance parameters was simulated using the computer code developed which was implemented in MATLAB. The results show that the engine speed of 3000 rpm gave the optimum values of 250 g/kWh, 33 kW, 1070 kPa, 28% and 720 oC for BSFC, BP, BMEP, TE, and EGT respectively. Also, all performance parameters increased with an increase in engine load. The equivalence ratio of 0.9 gave the optimum values for all the parameters considered in this work. It can be concluded that for optimum performance of non-road SI engines, it should be operated at equivalence ratio of 0.9, engine speed of 3000 rpm and low engine loads.