In the laboratory of Machines at the university of Gent a multi-point liquid LPG fuel injection system has been developed. The tests have shown that the LPG injection system works perfectly for all speed and load conditions of the engine. The advantages of LPG are confirmed with the tests: prevention of knock at high compression ratios, less exhaust gas pollutants. The tests were carried out on a standard Ford gasoline (injection) engine. Comparative tests are presented for the gasoline engine, the engine with an evaporation system (LPG and butane as fuels) and for the engine with the LPG injection system.
Then a parametric study of the LPG injection engine has been done (ignition timing, air-fuel ratio, compression ratio). The influences of these parameters on the engine characteristics are given (influences on power output, efficiency, fuel consumption, NOX concentration). A remarkable increase in the power output when the compression ratio is increased is noted.
Also, a heat release analysis is made for the LPG injection engine. Therefore a high pressure transducer was mounted flush with the combustion chamber wall; and cylinder pressure diagrams were obtained. A short description of the heat release analysis theory is given (based on the first law of thermodynamics). Instantaneous and cumulative rates of combustion for different engine conditions are presented, compared and discussed. Finally it is shown that the combustion phasing angle (crank angle for which 50% of the fuel is burnt) is a useful tool to optimize the engine parameters.