Comparative Analysis of Exhaust Emission of Retrofitted SI Engine Runs by Different Fuels

Abstract

The purpose of this study was to experimentally inspect the pollutant emission of a retrofitted SI engine using octane, compressed natural gas, and liquefied petroleum gas fuels operated at different speeds. The study was conducted using a retrofitted SI engine. The engine was coupled with an exhaust gas analyzer to measure the composition of the exhaust emission gas. The results showed that the carbon dioxide (CO2) and carbon monoxide (CO) content is lower when CNG is used compared to octane. The CO2 emission was even lower for LPG than CNG, as LPG has a lower carbon-energy ratio and higher octane quality than LPG and burns faster as a lean mixture. The O2 emission supports that octane and CNG burn as a lean mixture whereas LPG burns as rich. Again, the HC emissions are more prominent and CO emissions are higher for LPG than CNG. Because, it showed incomplete combustion with LPG as fuel due to inappropriate air-fuel mixture in the gas-air mixing chamber, which was specifically designed for CNG. Nitrogen oxide (NOx) emission was minimal when the engine was operated with LPG due to incomplete combustion, and it was found maximum for octane, where medium NOx content was found in the case of CNG. Moreover, the relative air fuel ratio or excess air factor, λ increased as the engine operating speed was raised. Because at high speed, there is some turbulence effect and increased combustion duration.