Experimental Analysis of a Single-Cylinder Large Bore Engine with External Supercharging in Diesel/ CNG Dual-Fuel Mode

The need for a quick reduction in greenhouse gasses and noxious emissions is pushing maritime transportation to increase the use of alternative fuels. Natural Gas (NG) is well recognized as an effective solution to limit the use of marine diesel oil in the short/mid-term. In this scenario, dual-fuel technology is used to enable a conventional diesel engine to operate with a share of gaseous fuel while retaining the capability to run in full diesel mode. Dual-fuel (DF) engines allow the use of natural gas, or biomethane from renewable sources, as the main fuel, with advantages over CO2, SOx and PM emissions with the same levels of NOx. This paper presents an experimental study investigating the effects of the diesel injection strategy on performance and emissions of a dual-fuel, single-cylinder, large bore, 4-stroke engine for marine applications. The engine is equipped with an external supercharging system; NG is injected in the port, while a Common Rail system injects the diesel pilot. Measurements were performed at 1500 rpm speed and Brake Mean Effective Pressure (BMEP) of 8.4 bar: the full diesel engine point representative of commercial Electronic Control Unit (ECU) map is chosen as reference. Further investigations will be performed to estimate the influence of dual-fuel combustion on the loss linked to the external supercharging. The performance of an externally supercharged and a turbocharged engine may differ: when working with turbocharged engines, boost and exhaust backpressure simultaneously increase. In contrast, when reproducing external supercharging behavior, an increase in the exhaust backpressure could alter the internal exhaust gas recycling and energy balances.