Effect of single-contact spark plug electrode gap on composition of engine exhaust emissions

Abstract

The spark plug is an important part of the spark ignition (SI) engine, which, like other parts, outwears over time, but its outwear stages are often not felt at all in everyday use. For spark plugs, the manufacturer has specified the service life under specific operating conditions. However, if both gasoline and liquefied petroleum gas (LPG) are used as fuel in the spark ignition engine, the spark plugs outwear in a shorter period of time. This is due to differences in combustion temperatures, which are affected by the octane number of the fuel. The main sign of spark plug outwear is an increase in the gap between the electrodes, which is directly related to the combustion of the fuel mixture. Consequently, the composition of the exhaust gases also changes. Therefore, a study was performed on the effect of single-contact spark plug electrode spacing on the exhaust gas composition of SI engine running on gasoline and LPG. For the study, Peugeot 407SW vehicle was used, manufactured in 2006 and equipped with a 2.0-liter SI engine, which was additionally equipped with a gas fuelling system. Spark plugs BOSCH FR7NI332S were used in the experiment. The study found that hydrocarbons and carbon monoxide in exhaust gases can increase significantly, while carbon dioxide changes are inessential.