Ignition timing

Summary

In a spark ignition internal combustion engine, ignition timing is the timing, relative to the current piston position and crankshaft angle, of the release of a spark in the combustion chamber near the end of the compression stroke. The need for advancing (or retarding) the timing of the spark is because fuel does not completely burn the instant the spark fires. The combustion gases take a period of time to expand and the angular or rotational speed of the engine can lengthen or shorten the time frame in which the burning and expansion should occur. In a vast majority of cases, the angle will be described as a certain angle advanced before top dead center (BTDC). Advancing the spark BTDC means that the spark is energized prior to the point where the combustion chamber reaches its minimum size, since the purpose of the power stroke in the engine is to force the combustion chamber to expand. Sparks occurring after top dead center (ATDC) are usually counter-productive (producing wasted

Official source

https://en.wikipedia.org/wiki/Ignition_timing

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Numerical simulations of a prechamber autoignition cogeneration engine operating on natural gas

Daniel Favrat, Stefan Heyne, Grégory Millot

A numerical simulation of a prechamber autoignition gas engine has been performed based on an experimental test case. With a simplified finite-rate/eddy-dissipation model for the combustion of natural gas, it was possible to properly reproduce the experiment considering the combustion duration, ignition timing and overall energy balance. However the predefined empiric constant of the eddy-dissipation model had to be increased by a factor of 10. A modification of the original cylindrical-conical prechamber geometry to a simpler cylindrical one was tested with the simulation model. The influence of burnt gases inside the prechamber was assessed simulating the mixture formation inside the prechamber. The simulations showed little effect of taking into account the non-homogeneities in the gas phase on the combustion duration. The simulation showed that the new and cylindrical geometry envisaged did not show any improvement in the combustion homogeneity inside the prechamber and its volume (limited by the real engine geometry) is in fact not sufficient to properly ignite the main chamber. The model can be used to further guide design modifications of the prechamber engine to improve performance.

2007

Numerical simulations of a prechamber autoignition cogeneration engine operating on natural gas

Daniel Favrat, Stefan Heyne, Grégory Millot

A numerical model for a prechamber autoignition gas engine under development has been established based on an experimental test case. With a simplified finiterate/ eddy-dissipation model for the combustion of natural gas, it was possible to properly reproduce the experiment considering the combustion duration, ignition timing and overall energy balance. The predefined empiric constant of the eddydissipation model had to be increased by a factor of 10. A modification of the original cylindrical-conical prechamber geometry to a simpler cylindrical one was tested with a simulation. The influence of burnt gases inside the prechamber was assessed simulating the mixture formation inside the prechamber. The simulations showed little effect of taking into account the non-homogeneities in the gas phase on the combustion duration. The cylindrical geometry tested did not show any improvement in the combustion homogeneity inside the prechamber and its volume (limited by the real engine geometry) is not sufficient to properly ignite the main chamber.

2009

Numerical Simulations of a Prechamber Autoignition Engine Operating on Natural Gas

Daniel Favrat, Stefan Heyne, Grégory Millot

At our laboratory extensive research has been conducted on the conversion of conventional Diesel cogeneration engines to operation on natural gas and biogas. In the framework of this research, a numerical simulation of a prechamber autoignition gas engine has been performed based on an experimental test case. With a simplified finite-rate/eddy-dissipation model for the combustion of natural gas, it was possible to properly reproduce the experiment considering the combustion duration, ignition timing and overall energy balance. A modification of the original cylindrical-conical prechamber geometry to a simpler cylindrical one was tested with the simulation model. The influence of burnt gases inside the prechamber was assessed simulating ghe mixture formation inside the prechamber. The simulations showed little effect of taking into account the non-homogeneities in the gas phase on the cumbustion duration. The new cylindrical geometry envisaged did not show any improvement in the combustion homogeneity inside the prechamber and its volume (limited by the real engine geometry) is in fact not sufficient to properly ignite the main chamber according to the simulations. The model can be used to further guide design modifications of the prechamber engine to improve performance.

2011