Influence of Commercial Gasoline Samples on the PerformanceCharacteristics of SI Engines

It has been observed though not documented that some gas filling stations in Nigeria adulterate their fuel before selling to customers. Numerous engine users had also complained of fuel obtained from some petrol filling stations burn faster than others. Engines used in automobile vehicles and power plants always developed one fault or the other leading to frequent visit to mechanics. In view of these preceding issues, experimental study was conducted to determine the influence of gasoline sold in Nigeria market on engine performance characteristics. Four samples of commercial gasoline were collected from different petrol stations within Omu-Aran metropolis, Kwara State, Nigeria and tested on a four stroke single cylinder spark ignition engine (P8161) automotive test bed at wide throttle opening. However, the octane rating of the selected fuel samples could not be ascertain because gasoline supplied at Nigeria petrol stations are no longer rated as it used to be as regular, premium and regular unleaded. The results of this investigation show that the performance parameters such as torque, brake power, brake mean effective pressure and thermal efficiency for each fuel sample increase with increase engine speed up to a maximum value and begin to decrease as engine speed increase due to frictional loss. Maximum brake power obtained with fuel sample A was 5.751 kW at 3083 rpm. For fuel sample B, the maximum brake power was 5.025kW at 2884 rpm, 5.269 kW at 2727 for fuel sample C and 5.019 kW at 2718 rpm for fuel sample D. From this test, brake maximum power and torque occur at the same engine speed for each sample of fuel sample studied. Also the maximum power obtained from fuel sample B and D were approximately the same at different engine speed. It may suffice to say that fuel sample B and D were likely supplied to the different petrol filling stations by the same source. The minimum amount of fuel consumed in order to attain maximum power was more with fuel sample D and B corresponding to 36.73 g/kW.hr and 36.63 g/kW.hr respectively. The minimum brake specific fuel consumption was lower for fuel sample A and C with value 32.21 g/kW.hr and 35.44 g/kW.hr respectively. Therefore, it is more economical and reliable to run spark ignition engines with fuel sample A and C. Analysis of fuel variability shows that the coefficient of variation in engine speed for fuel sample A, B, C and D were 32.6%, 34.2%, 33.1% and 35.2% respectively. In terms of brake power developed the coefficients of variation were 52.2%, 56%, 53.8% and 60.6% for fuels A, B, C and D respectively. The coefficient of variation in terms brake specific fuel consumption are 101.3%, 142.8%, 111.5% and 131.9% for fuel samples A, B, C and D respectively. It means that more of fuel B was consumed follow by fuel sample D during the combustions process compared to fuel samples A and C. For fuel sample B approximately 43% additional fuel is required to attain the maximum power and about 32% of fuel sample D. Approximately 12% additional of fuel sample C is required while only 2% of fuel sample A is needed. From the results fuel sample A is more reliable for achieving engine performance specifications follow by fuel sample C and B while fuel sample D is less reliable. One of the factors that may be responsible for the variation is fuel octane rating which is a measure of how smooth an engine runs or resistance to knocking. If this is true, engines running on fuel samples D and B are more prone to pre-ignition or engine knock than fuel sample A and C. It then means there is strong relationship between fuel samples and engine performance.