The concentration of a chemical species in vehicle exhaust is a function of several factors, including engine type, engine operating conditions, fuel and lubricating oil composition and emission control system ( Johnson, 1988). These incomplete combustion products comprise thousands of chemical components present in the gas and particulate phases ( Zaebst et al., 1988) some specific chemical species and classes found in engine exhausts are listed in Table 1. Incomplete combustion results in the emission of carbon monoxide, unburnt fuel and lubricating oil ( Yamaki et al., 1986) and of oxidation and nitration products of the fuel and lubricating oil. Gasoline engines are designed to operate at a nearly stoichiometric ratio (air:fuel ratio, ≃14.6:1) diesel engines operate with excess air (air:fuel ratio, ≃25–30:1 Lassiter & Milby, 1978). Some excess oxygen may be emitted, depending on the operating conditions of the engine. A very small portion of the nitrogen is converted to nitrogen oxides and some nitrated hydrocarbons. The major products of the complete combustion of petroleum-based fuels in an internal combustion engine are carbon dioxide (13%) and water (13%), with nitrogen from air comprising most (73%) of the remaining exhaust.
There are two categories of diesel engine: open-chamber or direct-injection engines are preferred for heavy-duty applications because they offer the best fuel economy divided-chamber or indirect-injection engines have been preferred for light-duty applications because they are less sensitive to differences in fuels, have a wider range of speeds (and therefore greater power:weight ratio), run more quietly and emit fewer pollutants ( National Research Council, 1982). Primarily because of its higher density, a litre of diesel fuel contains approximately 13% more energy than a litre of gasoline. The fuels used in diesel and gasoline engines also differ, with diesel fuel consisting of higher boiling range petroleum fractions (see IARC, 1989). In gasoline engines, the fuel is ignited by sparking-plugs. In diesel engines, the fuel is self-ignited as it is injected into air that has been heated by compression. They are both internal, intermittent combustion engines.
The engine speed of 4000 rpm at Maximum Brake Torque (MBT) produced the most nearest results to gasoline.Diesel and gasoline engines are the major power train sources used in vehicles. Burn rate shows why CNG had a slower burning speed on the small engine. Pressure analysis shows peak pressure dropped by 16%. The comparison shows a drop of 18.6% was seen for the power, brake specific fuel consumption (BSFC) loss was 7% and efficiency loss was at 17.3% in average for all engine speed.
The results were analyzed for burn rate based on the first law of thermodynamic. The emissions readings were also compared from an emission analyzer. Measurements of engine speed, torque and fuel were done on an eddy current dynamometer, while measurements or in-cylinder pressure, crank angle and spark were analyzed from results taken by data acquisition system. A bi-fuel sequential system was used to do this evaluation. The main focus of this paper was to evaluate a sub compact car engine for its performance and burn rate of gasoline and Compressed Natural Gas (CNG). In term of subcompact cars, the vehicle characteristics are governed by the engine for alternative fuels. Vehicle efficiency relates to pollutants and cost savings in third world countries.