F2010A062
Heat Transfer Measurements Inside a Gas Fuelled Spark Ignited Engine for Model Validation
The search for alternative fuels has led to the use of gas fuelled engines. Liquefied petroleum gas and especially natural gas are already widespread because they increase the energy security, give lower CO2 and noxious emissions and have a higher knocking resistance. They are still fossil fuels so sustainable alternatives like hydrogen are also investigated. Computer simulation of the engine cycle enables a cheap and fast optimization of engine settings. Accurate emission calculations are a prerequisite as the control of emissions is an important boundary condition for power and efficiency optimization. Modelling the heat transfer from the burning gases to the cylinder walls is an indispensable keystone. Existing heat transfer models from Annand and Woschni were developed for diesel and gasoline and need to be validated for gaseous fuels in general and hydrogen more specifically. The models are expected to be inaccurate for hydrogen combustion because of its higher laminar flame velocity, shorter quenching distance and higher thermal capacity which increase the heat transfer. In this paper transient heat flux is evaluated at the cylinder liner of a spark ignited CFR engine with a Vatell Heat Flux Microsensor for validation of the existing models of Annand and Woschni. The influence of the compression ratio, measuring position, spark timing and mixture richness is investigated. Measurements are executed on hydrogen and on methane for fuel comparison. Less cyclic and spatial variation in the heat flux traces are observed when burning hydrogen, which can be correlated to the burn rate. The heat flux increases with compression ratio and mixture richness. Advanced spark timing causes an increased and advanced peak in the heat flux trace. Hydrogen combustion gives a heat flux peak which is three times as high as the one of methane for the same engine power output. Some parameters within the heat transfer models can be changed to tune them for a certain engine. For methane combustion these parameters only have to be adjusted slightly to predict the heat transfer peak within the boundary of the measurement uncertainty. The model of Annand however, tends to overestimate the heat transfer in the compression and expansion stroke. This is not the case for Woschni's model. Both models fail to calculate the heat transfer for hydrogen combustion. The aforementioned parameters have to be set above unity in order to predict the heat transfer within the boundary of the measurement uncertainty. This demonstrates the models lack some fuel properties which influence the heat transfer process in the case of hydrogen combustion.
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Session: IC Engines, Goals and Development