This paper presents the results of the experiments conducted on a spark-ignition (SI) engine fuelled with
liquefied petroleum gas (LPG) by varying the ignition timing at the excess air coefficients of 1.0 and 1.3.
Experiments were carried out at wide open throttle (WOT) position and at engine speed of 4300 rpm
aiming to determine the lean operation performance of an engine when fuelled with LPG at full load.
Performance parameters, namely brake power, brake-specific fuel consumption (BSFC), brake thermal
efficiency and exhaust emissions such as unburned hydrocarbons (HC), carbon monoxide (CO) and nitrogen
oxides (NOx), were studied. It was shown that advancing the ignition timing improved the performance
of LPG-fuelled SI engine for excess air coefficients higher than 0.8. The highest brake power and
the lowest BSFC were obtained with modified ignition timing at an excess air coefficient of 1.0. The
lowest exhaust emissions were obtained with an excess air coefficient of 1.3. In general, advancing the
ignition timings caused increase in HC and NOx emissions, while the effect of ignition timing on CO
emissions was negligible.