Experimental measurements of the laminar burning velocity are mostly limited in pressure and temperature and can be compromised by the effects of flame stretch and instabilities. Computationally, these effects can be avoided by calculating one-dimensional, planar adiabatic flames using chemical oxidation mechanisms. Chemical kinetic models are often large, complex and take a lot of computation time, and few models exist for multi-component fuels. The aim of the present study is to investigate if simple mixing rules are able to predict the laminar burning velocity of fuel blends with a good accuracy. An overview of different mixing rules to predict the laminar burning is given and these mixing rules are tested for blends of hydrocarbons and ethanol. Experimental data of ethanol/n-heptane and ethanol/n-heptane/iso-octane mixtures and modeling data of an ethanol/nheptane blend and blends of ethanol and a toluene reference fuel are used to test the different mixing rules. Effects of higher temperature and pressure on the performance of the mixing rules are investigated. It was found that simple mixing rules that consider only the change in composition are accurate enough to predict the laminar burning velocity of ethanol/hydrocarbon blends. For the blends used in this study, a Le Chatelier's rule based on energy fractions is preferable because of the similar accuracy in comparison to other mixing rules while being more simple to use.

The use of biomass-derived ethanol in spark-ignition engines is an interesting op-10 tion to decarbonize transport and increase energy security. An engine cycle code valid for this fuel, could help to explore its full potential. Crucial building blocks to model the combustion in ethanol engines are the laminar burning velocity and flame thickness of the ethanol-air-residuals mixture at instantaneous cylinder pressure and temperature. This information is often implemented in engine codes using correlations. A literature 15 survey showed that the few available flame thickness correlations have not yet been validated for ethanol. Also, none of the existing ethanol laminar burning velocity correlations covers the entire temperature, pressure and mixture composition range as encountered in spark-ignition engines. Moreover, most of these correlations are based on measurements that are compromised by the effects of flame stretch and the occurrence 20 of flame instabilities. For this reason, we started working on new correlations based on flame simulations using a one-dimensional chemical kinetics code.In this paper the published experimental data for the laminar burning velocity of ethanol are reviewed. Next, the performance of several reaction mechanisms for the oxidation kinetics of ethanol-air mixtures is compared. The best performing mecha-25 nisms are used to calculate the laminar burning velocity and flame thickness of these mixtures in a wide range of temperatures, pressures and compositions. Finally, based on these calculations, correlations for the laminar burning velocity and flame thickness covering the entire operating range of ethanol-fuelled spark-ignition engines, are presented. These correlations can now be implemented in an engine code.

No abstract

No abstract

Diesel spray experimentation at controlled high-temperature and high-pressure conditions is intended to provide a more fundamental understanding of diesel combustion than can be achieved in engine experiments. This level of understanding is needed to develop the high-fidelity multi-scale CFD models that will be used to optimize future engine designs. Several spray chamber facilities capable of high-temperature, high-pressure conditions typical of engine combustion have been developed, but because of the uniqueness of each facility, there are uncertainties about their operation. The Engine Combustion Network (ECN) is a worldwide group of institutions using combustion vessels, whose aim is to advance the state of spray and combustion knowledge at engine-relevant conditions. A key activity is the use of spray chamber facilities operated at specific target conditions in order to leverage research capabilities and advanced diagnostics of all ECN participants. The first target condition, called "Spray A", has been defined with detailed ambient and injector conditions. For this paper, we describe results from the constant-volume pre-burn vessel at Eindhoven University of Technology. The executed measurements include a wide range of diagnostics to characterize "spray A" in reacting and non-reacting conditions in great detail. Observations of spray penetration, ignition, liquid length and flame lift-off location by using several high-speed imaging diagnostics are discussed and compared with other ECN participating institutes. Comparison Spray A data from the other participating institutes, as it was presented during the 2 nd ECN workshop is gathered from the ECN website database [1]. It can be concluded that the obtained results from the standardized ECN spray diagnostics, show satisfactory similarity, despite of the challenge to reach similar boundary conditions (ambient and injector) in each of the unique facilities. The differences in results are within the measurement deviation and uncertainty or can be explained by the usage of (slightly) different injectors. Combining the results of the different measurement techniques provides an overall (time resolved) overview where the different phases of fuel injection are directly linked and summarized. The presented overview provides a direct input for (CFD) modeling validation.