Abstract
Dual fuel engines induce benefits in terms of pollutant emissions of PM and NOx together with carbon dioxide reduction and being powered by natural gas (mainly methane) characterized by a low C/H ratio. Therefore, using natural gas (NG) in diesel engines can be a viable solution to reevaluate this type of engine and to prevent its disappearance from the automotive market, as it is a well-established technology in both energy and transportation fields. It is characterized by high performance and reliability. Nevertheless, further improvements are needed in terms of the optimization of combustion development, a more efficient oxidation, and a more efficient exploitation of gaseous fuel energy. To this aim, in this work, a CFD numerical methodology is described to simulate the processes that characterize combustion in a light-duty diesel engine in dual fuel mode by analyzing the effects of the changes in engine speed on the interaction between fluid-dynamics and chemistry as well as when the diesel/natural gas ratio changes at constant injected diesel amount. With the aid of experimental data obtained at the engine test bench on an optically accessible research engine, models of a 3D code, i.e., KIVA-3V, were validated. The ability to view images of OH distribution inside the cylinder allowed us to better model the complex combustion phenomenon of two fuels with very different burning characteristics. The numerical results also defined the importance of this free radical that characterizes the areas with the greatest combustion activity.
Highlights
The diesel engine has always played a central role in the energy and transportation sectors
It is interesting to notice how the distributions prepresent the same shape: the two cases being performed at the same engine speed confirm sentthe thesame sameshape: shape:the thetwo twocases casesbeing beingperformed performed the same engine speed confirm that sent atat the same engine speed confirm that that the same swirl motion been established inside the cylinder, show the involvement thesame same swirl motion hashas been established inside the cylinder, show involvement the swirl motion has been established inside the cylinder, show thethe involvement of of of the same regions the oxidation process
Since the Total fuel burning rate (FBR) takes the consumption of both fuels into account, this may be due to the full activation of methane combustion
Summary
The diesel engine has always played a central role in the energy and transportation sectors. Results showed that increasing the rotational speed can exert a relevant influence on a number of time-dependent processes such as liquid fuel injection and atomization, the mixing of reactant species, and chemical kinetics; a proper choice in the injection setting can help to achieve ignition in each zone of the combustion chamber. In this way, it is possible to obtain an efficient use of the chemical and energetic contents of the fuel, with a consequent reduction of the emissions of unburned hydrocarbons in the exhaust. An experimental validation is attained through the comparison of numerical results with experimental tests conducted on a single-cylinder research engine
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