Carburetion and Port Fuel Injection Metering Strategies for Natural Gas Spark-Ignited Engine

Abstract

The effects of carburetion and port fuel injection (PFI) metering techniques were experimented on naturally aspirated twin-cylinder spark-ignited (SI) engine fuelled with compressed natural gas (CNG). It was operated under full throttle condition at varying speeds ranging from 920 to 3400 rpm for the compression ratio 11.5:1. The performance, emission and combustion parameters were assessed and compared. The carburetion was set at 0.9 bar, while the PFI was set to 5 bar working pressure. A dedicated electronic control unit (ECU) was used for controlling the engine parameters. Comparing with carburetion, the PFI produced maximum brake thermal efficiency of 27.2% at 1800 rpm. Due to the increased volumetric efficiency performance of PFI system, there was notable reduction in hydrocarbon (HC) as well as carbon monoxide (CO) emissions in comparison with carburetion. There was a noticeable increase in nitric oxide (NO) emission as a result of complete combustion. The enhanced combustion process with PFI has improved peak pressure with reduced cyclic variations. On a whole, PFI system had excelled carburetion system towards better mixture formation.