A holistic investigation of natural gas–diesel dual fuel combustion with dual direct injection for passenger car applications

Abstract

This publication covers the investigation of a dual fuel combustion process for passenger car applications using natural gas and diesel as fuels. In the literature a widely studied dual fuel concept is the combination of port fuel injection of natural gas and direct injection of diesel. The challenge of this concept is a high emission of unburned hydrocarbons at low load operation as previous publications show. The proposed concept features a low pressure direct injection of natural gas in combination with direct injection of diesel to circumvent this problem. The acronym DDI-dual direct injection is introduced for this concept. It enables charge stratification of the air-natural gas mixture. This allows for a significant reduction of the unburned hydrocarbon emissions as earlier studies already demonstrated. The focus of this publication is on hardware variations which were performed on the engine test bench. Results are presented of a variation of the compression ratio and of different charge motion patterns which were studied. The results are compared with a conventional diesel and a gasoline spark ignited engine. The investigations demonstrate that a CO 2 reduction of 20-29% is feasible as compared to conventional engines. Finally, investigations of exhaust gas aftertreatment with a threeway catalyst are published. The aftertreatment of the remaining engine-out hydrocarbon emissions is still the key challenge due to the low exhaust gas temperature during low load operation.

Future Power Train Solutions for Long-Haul Trucks

“…Another possibility for direct injection is low-pressure direct injection of around 16 bar. Fasching et al [168] performed a detailed analysis of this concept and reported that further studies must be performed in order to reduce engine-out and tailpipe methane emissions.…”

Simulation Modeling of a Dual Fuel (Natural Gas-Diesel) Engine Using Early Direct Injection Technique of Natural Gas

“…The mass flow rate of injected NG is simulated as a chocked flow through a singlehole injector. The chocking condition is practically chosen for NG injection since it ensures stable injection [15]. The injection pressure of NG is chosen to be equal 10 bar since this value can maintain a critical pressure ratio through the injector nozzle for the selected injection timing, which is equal to IVC, and engine loads.…”

“…The benefits include improvements in thermal efficiency through increasing the flame speed of NG resulting from the combustion of locally stoichiometric NG-air mixture [13]. However, the main drawbacks of this method include the increased complexity of the injection system due to the high injection pressure and the increase in soot emissions due to the presence of rich mixture zones [14,15]. Engine simulations are valuable tools for evaluating the performance and emission parameters.…”