Effect of Spark Advance on a Gas Run Automotive Spark Ignition Engine

Abstract

Petrol engines can run on natural gas, with little modification. The combustion characteristics of natural gas is different from that of petrol, which eventually affects the engine performance. The performance of a typical automotive engine was studied running on natural gas, firstly at a constant speed for various loads and then at a constant load for a range of speeds and results were compared with performance using petrol. Variation of the spark advance, consisting of centrifugal and vacuum advance mechanisms, was investigated. Results showed some reduction in power and slight fall of efficiency and higher exhaust temperature, for natural gas. The air-fuel ratio for optimum performance was higher for gas than for petrol. This variation in spark requirement is mainly due to the slower speed of flame propagation for natural gas. For both the cases, the best power spark advance for natural gas was found to have higher values than petrol. This issue needs to be addressed during retrofitting petrol engines for running on natural gas.

Technical overview of compressed natural gas (CNG) as a transportation fuel

“…This lower flame propagation speed conduce to prolongation in total combustion duration compared with gasoline/diesel and allows exit of a greater amount of unburned natural gas through the exhaust [32]. Due to this low speed of the flame, when the when the engine fueled by CNG engine operates closely to the lean limit, problem of misfiring happens.…”

“…They observed that the volumetric efficiency and brake power of CNG fueled engine was low than that of gasoline engine. Ehsan [32] studied the effect of variation of spark advance on the performance of a typical bi-fuel 4-cylinder, 1600 cm 3 carburetor car engine. According to his results, maximum engine power produced when running on natural gas was 5-10% lower compared to when running on gasoline.…”

“…On the other hand, liquid fuel needs time for complete atomization and vaporization to form a homogeneous air-fuel mixture [25]. CNG being a gaseous fuel at normal atmospheric conditions has the inherent advantage of high level of miscibility and diffusion with gaseous air, which is essential for good combustion [32].…”

“…As the world continues to operate with costly fuels such as diesel and gasoline, the low cost CNG provides a spark of hope. Although the environmental aspects and emission control of using CNG was the prime objective of natural gas application in road transport, especially inside big cities, in recent days with sharp rise in oil prices, the increasingly significant economic advantage of using CNG has become the real prime consideration for lot of new users [32]. In most countries, CNG is much cheaper per equivalent gallon than gasoline and diesel, even after considering the costs associated with compression and so even taking into account its lower thermal efficiency to diesel and gasoline there are considerable economic advantages of using CNG as a transportation fuel.…”

Natural Gas Engine Technologies: Challenges and Energy Sustainability Issue

“…There is a lack of consistency on ignition advances for MBT of CNG in the literature. Bell et al (1993), as cited by Ehsan (2006), reported it as 15-20 • CA more than that of gasoline [214,215]. This value was contradicted by Cho and He (2007), placing it at 2-10 • CA more than that of gasoline [9].…”