ANALYSIS AND COMPARISON ON EFFECT OF AIR-FUEL RATIO TOWARDS THE FOURSTROKE SINGLE CYLINDER ENGINE PERFORMANCE

Abstract

The present study focuses on the effect of different air-fuel ratio (AFR) toward the four-stroke 150cc single cylinder piston engine power output. AFR is the mass ratio of air to fuel present in a combustion process such as in an internal combustion engine. The AFR is an important measure for anti-pollution and performance-tuning reasons. If exactly enough air is provided to completely burn all of the fuel, the ratio is known as the stoichiometric mixture, often abbreviated to “stoich”. AFR numbers lower than stoichiometric are considered "rich". Rich mixtures are less efficient, but may produce more power and burn cooler, which is kinder on the engine. AFR numbers higher than stoichiometric are considered "lean." Lean mixtures are more efficient but may cause engine damage or premature wear and produce higher levels of nitrogen oxides. In theory, a stoichiometric mixture has just enough air to completely burn the available fuel. In this experiment, the main point of the study is to collect the data of the Yamaha Y15ZR engine performance with the various value of AFR by carry out the test using dynamometer laboratory. Engine performance is evaluated based on their horsepower and torque that are produced by the engine. Good engine performance result is generated from good adjustment of AFR, ignition timing and engine setup. During the dynamometer test, there are several adjustments needed to be conduct such as, amount of fuel injection, air screw and any other adjustment to achieve the set value of AFR by tuning it on programmable engine control unit (ECU). The AFR value is based on Lambda Oxygen (O₂) sensor in exhaust manifold. The result had been taken during dynamometer test by taking the record on horsepower, torque, carbon monoxide (CO), carbon dioxide (CO₂) and exhaust air temperature. The difference between the highest engine power output compare to the stoichiometric mixture power output is 3.3 horsepower gain. This makes a significant difference to the performance of the engine also consume less throttle compare to the stoichiometric mixture. This is because the rider just slightly open small amount of throttle to get the desired power. According to the tuner found that the throttle response of using AFR 12.5:1 is much better compare to the stoichiometric ratio.