Abstract
Both greenhouse gas (GHG) emissions and local emissions from heavy duty (HD) Diesel engines must be greatly reduced to make transportation sustainable and comply with increasingly stringent emissions regulations. The fuel flexible engine concept for HD Diesel engines uses a dual fuel direct injection system in which ignition of the main alcohol fuel, either methanol or ethanol, is induced by a small Diesel pilot injection delivered via a separate direct injector. The objective of this investigation was to find ways to combine the advantages of conventional Diesel engines with the advantages of low carbon fuels and to thereby bypass the soot-NOx-trade-off. Experiments were conducted using a modified single-cylinder HD engine and three fuels (methanol, ethanol, and a reference Diesel fuel) to determine how the choice of fuel affected the engine’s combustion behaviour, emissions and fuel efficiency. Injection pressures on the alcohol side were varied up to 1500 bar and the investigation was carried out at low, medium and high speed-load points. The alcohol fuels significantly outperformed Diesel fuel under all tested conditions (with and without exhaust gas recirculation (EGR)). Indicated thermal efficiency was increased by up to 3.5%-points and simultaneously soot emissions were lowered by a factor of 40 or more and NOx by 20%. Combustion stability and emissions were in the same range as for Diesel but replacing more than 95 % of the fossil Diesel with an alcohol fuel.
Highlights
The demand for transportation has increased significantly in recent decades because of the rising global population, the growing middle class in developing countries, more extensive global trade, and urbani zation
The injection technique proposed here is similar to direct dual fuel strat ification (DDFS) but the combustion strategy is more closely related to that used in conventional Diesel engines, which means that combustion mainly driven by diffu sion
The flow number of the main injector was increased from 2.3 l/ min at 100 bar to 4.6 l/min to adjust the injected energy per time unit in order to account for the lower lower heating value (LHV) of methanol; the same injector was used for ethanol
Summary
The demand for transportation has increased significantly in recent decades because of the rising global population, the growing middle class in developing countries, more extensive global trade, and urbani zation. One way to reduce emissions from heavy duty (HD) ICEs is to replace fossil Diesel fuel with low carbon alcohol based-alternatives. Considerable effort has been invested into developing low temperature combustion (LTC) concepts that simultaneously reduce soot and NOx emissions. Dual fuel strategies have been developed using an additional port fuel injection system for the low cetane fuel and direct Diesel in jection to facilitate ignition [15]. These strategies can be implemented for various combustion modes and have the potential to reduce both soot. Indicated Thermal Fuel Efficiency Hydrocarbons Apparent Rate of Heat Release Combustion phasing (50 % of fuel combusted) End of Combustion (90 % of fuel combusted) Computational Fluid Dynamics Heat Release Combustion Progress Variable Effective Expansion Ratio Indicated Mean Effective Pressure Coefficient of Variation Crank Angle Degrees After Top Dead Center Crank Angle Degrees Before Top Dead Center End of Injection Fuel Substitution Ratio
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