Study of the Performance and Emissions of a Methane Fueled V-Twin Four Stroke Spark Ignited Engine

Abstract

This paper discusses the on-going study of a modified two-cylinder V-twin engine used to research and analyze natural gas combustion. The purpose of the experimentation is to determine the feasibility of Natural Gas as an alternative fuel for automotive and stationary power generation applications. During testing the engine was operated under various loads and RPMs. The compression ratio (CR) of the engine was increased from 9.0:1 to 13.8:1 with the expectation of improved fuel combustion and improved emissions. The Exhaust Gas Recirculation (EGR) and air-fuel ratio (AFR) were also varied to determine optimal levels that would improve emissions without compromising excessive power (hp). Lean limit analysis was conducted to understand the effect of increased AFR on combustion and emissions. Results from testing confirmed an emissions benefit of going from low compression to high compression. The Total Hydrocarbons (THC) decreased 25%, Carbon Monoxide levels decrease by 48% and the Oxides of Nitrogen (NOx) decreased by 20%. A low percentage of EGR, between 3-6 %, helped reduce Oxides of Nitrogen (NO_x) emissions from over 830 ppm to less than 450 ppm, an improvement of almost 50%, with less than a 2% increase in THC and CO. Power (hp) actually improved by about 1.5% with 3% EGR.  Increasing the AFR proved to decrease emissions but at a cost of power and the lean limit of the engine was found to be between 22 and 23 AFR. At 22 AFR the THC emissions decreased by 40%, CO emission by 90% and NOx emissions by almost 50%, but the power decreased by over 35%.