Joachim Demuynck

Laminar Burning Velocity Correlations for Methanol-Air and Ethanol-Air Mixtures Valid at SI Engine Conditions

The use of methanol and ethanol in spark-ignition (SI) engines forms a promising approach to decarbonizing transport and securing domestic energy supply. The physico-chemical properties of these fuels enable engines with increased performance and efficiency compared to their fossil fuel counterparts. An engine cycle code valid for alcohol-fuelled engines could help to unlock their full potential. However, the development of such a code is currently hampered by the lack of a suitable correlation for the laminar flame speed of alcohol-air-diluent mixtures. A literature survey showed that none of the existing correlations covers the entire temperature, pressure and mixture composition range as encountered in spark-ignition engines. For this reason, we started working on new correlations based on simulations with a one-dimensional chemical kinetics code. In this paper the properties of methanol and ethanol are first presented, together with their application in modern SI engines. Then, the published experimental data for the laminar burning velocity are reviewed. Next, the performance of several reaction mechanisms for the oxidation kinetics of methanol- and ethanol-air mixtures is compared. The best performing mechanisms are used to calculate the laminar burning velocity of these mixtures in a wide range of temperatures, pressures and compositions. Finally, based on these calculations, two laminar burning velocity correlations covering the entire operating range of alcohol-fuelled spark-ignition engines, are presented. These correlations can now be implemented in an engine code.

Applying Design of Experiments to Determine the Effect of Gas Properties on In-Cylinder Heat Flux in a Motored SI Engine

Models for the convective heat transfer from the combustion gases to the walls inside a spark ignition engine are an important keystone in the simulation tools which are being developed to aid engine optimization. The existing models have, however, been cited to be inaccurate for hydrogen, one of the alternative fuels currently investigated. One possible explanation for this inaccuracy is that the models do not adequately capture the effect of the gas properties. These have never been varied in a wide range because air and ‘classical’ fossil fuels have similar values, but they are significantly different in the case of hydrogen. As a first step towards a fuel independent heat transfer model, we have investigated the effect of the gas properties on the heat flux in a spark ignition engine. The effect of the gas properties was decoupled from that of combustion, by injecting different inert gases (helium, argon, carbon dioxide) into the intake air flow of the engine under motored operation. This paper presents the results of the experiment, which was designed with DoE techniques. The paper shows that the three investigated effects (throttle position, compression ratio and gas) and the interaction between the throttle and the compression ratio are significant with a significance level of 1%. Both the individual and combined effects of the gas properties are investigated. The most remarkable effect observed in the data was that the dynamic viscosity influences the heat flux in two contrasting ways. At the one hand, it increases the heat flux by increasing the gas temperature, at the other hand, it reduces the heat flux through the convection coefficient. A preliminary test shows that modeling under motored operation could be based on classical concepts. However, some scatter occurs in the data which needs further investigation.

Update on the Progress of Hydrogen-Fueled Internal Combustion Engines

This chapter provides an overview on the use of hydrogen as a fuel for internal combustion engines (ICEs). First, pros and cons are discussed for using hydrogen to fuel ICEs versus fuel cells. Then, the properties of hydrogen pertinent to engine operation are briefly reviewed, after which the present state of the art of hydrogen engines is discussed. Ongoing research efforts are highlighted next, which primarily aim at maximizing engine efficiency throughout the load range, while keeping emissions at ultralow levels. Finally, the challenges for reaching these goals and translating laboratory results to production are discussed.

Investigation of Supercharging Strategies for PFI Hydrogen Engines

Hydrogen-fueled internal combustion engines (H2 ICEs) are an affordable, practical and efficient technology to introduce the use of hydrogen as an energy carrier. They are practical as they offer fuel flexibility, furthermore the specific properties of hydrogen (wide flammability limits, high flame speeds) enable a dedicated H2 ICE to reach high efficiencies, bettering hydrocarbon-fueled ICEs and approaching fuel cell efficiencies. The easiest way to introduce H2 ICE vehicles is through converting engines to bi-fuel operation by mounting a port fuel injection (PFI) system for hydrogen. However, for naturally aspirated engines this implies a large power penalty due to loss in volumetric efficiency and occurrence of abnormal combustion. The present paper reports measurements on a single cylinder hydrogen PFI engine equipped with an exhaust gas recirculation (EGR) system and a supercharging set-up. The measurements were aimed at increasing the power output to gasoline engine levels or higher, while maximizing efficiency and minimizing emissions. Two strategies were tested: one using stoichiometric mixtures, with or without EGR, where a three way catalyst (TWC) was relied upon for aftertreatment of oxides of nitrogen (NOx ); and a second one using lean mixtures limiting engine-out NOx emissions so that aftertreatment was not needed. Test results are reported for varying supercharging pressure and engine speed, it is shown that both strategies allow power outputs exceeding gasoline levels. The brake thermal efficiencies for both strategies are compared, to derive the best operating strategy as a function of torque demand and engine speed. It can be concluded that the lean burn supercharged strategy is best overall.

Numerical Study of Flow Deflection and Horseshoe Vortices in a Louvered Fin Round Tube Heat Exchanger

In louvered fin heat exchangers, the flow deflection influences the heat transfer rate and pressure drop and thus the heat exchangers performance. To date, studies of the flow deflection are two-dimensional, which is an acceptable approximation for flat tube heat exchangers (typical for automotive applications). However, in louvered fin heat exchangers with round tubes, which are commonly used in air-conditioning devices and heat pumps, the flow is three-dimensional throughout the whole heat exchanger. In this study, three-dimensional numerical simulations were performed to investigate the flow deflection and horseshoe vortex development in a louvered fin round tube heat exchanger with three tube rows in a staggered layout. The numerical simulations were validated against the experimental data. It was found that the flow deflection is affected by the tubes in the same tube row (intratube row effect) and by the tubes in the upstream tube rows (inter-tube row effect). Flow efficiency values obtained with two-dimensional studies are representative only for the flow behavior in the first tube row of a staggered louvered fin heat exchanger with round tubes. The flow behavior in the louvered elements of the subsequent tube rows differs strongly due to its three-dimensional nature. Furthermore, it was found that the flow deflection affects the local pressure distributions upstream of the tubes of the downstream tube rows and thus the horseshoe vortex development at these locations. The results of this study are important because the flow behavior is related to the thermal hydraulic performance of the heat exchanger.

Evaluation of heat transfer models with measurements in a hydrogen-fuelled spark ignition engine

Hydrogen-fuelled internal combustion engines are still investigated as an alternative for current drive trains because they have a high efficiency, near-zero noxious and zero tailpipe greenhouse gas emissions. A thermodynamic model of the engine cycle enables a cheap and fast optimization of engine settings for operation on hydrogen. The accuracy of the heat transfer sub model within the thermodynamic model is important to simulate accurately the emissions of oxides of nitrogen which are influenced by the maximum gas temperature. These emissions can occur in hydrogen internal combustion engines at high loads and they are an important constraint for power and efficiency optimization. The most common models in engine research are those from Annand and Woschni, but they are developed for fossil fuels and the heat transfer of hydrogen differs a lot from the classic fuels. We have measured the heat flux and the wall temperature in an engine that can run on hydrogen and methane and we have investigated the accuracy of simulations of the heat transfer models. This paper describes an evaluation of the models of Annand and Woschni with our heat flux measurements. Both models can be calibrated to account for the influence of the specific engine geometry on the heat transfer. But if they are calibrated for methane, they fail to calculate the heat transfer for hydrogen combustion. This demonstrates the models lack some gas or combustion properties which influence the heat transfer process in the case of hydrogen combustion.

Applying Design of Experiments to Develop a Fuel Independent Heat Transfer Model for Spark Ignition Engines

Models for the convective heat transfer from the combustion gases to the walls inside a spark ignition engine are an important keystone in the simulation tools which are being developed to aid engine optimization. The existing models are, however, inaccurate for an alternative fuel like hydrogen. This could be caused by an inaccurate prediction of the effect of the gas properties. These have never been varied in a wide range before, because air and ‘classical’ fossil fuels have similar values, but they are significantly different in the case of hydrogen. We have investigated the effect of the gas properties on the heat flux in a spark ignition engine by injecting different inert gases under motored operation and by using different alternative fuels under fired operation. Design of Experiments has been applied to vary the engine factors in a systematic way over the entire parameter space and to determine the minimum required amount of combinations. This paper presents the validation of a heat transfer model based on the Reynolds analogy for the entire experimental dataset. The paper demonstrates that the heat flux can be accurately predicted during the compression stroke with a constant characteristic length and velocity, if appropriate polynomials for the gas properties are used. Furthermore, it shows that a two-zone combustion model needs to be used as a first step to capture the effect of the flame propagation. However, alternative characteristic lengths and velocities will need to be investigated to capture the intensified convective heat transfer caused by the propagating flame front and to accurately predict the heat flux during the expansion stroke.

Development and Validation of a Quasi-Dimensional Model for (M)Ethanol-Fuelled SI Engines

Methanol and ethanol are interesting spark ignition engine fuels, both from a production and an end-use point of view. Despite promising experimental results, the full potential of these fuels remain to be explored. In this respect, quasi-dimensional engine simulation codes are especially useful as they allow cheap and fast optimization of engines. The aim of the current work was to develop and validate such a model for methanol-fuelled engines. Several laminar burning velocity correlations and turbulent burning velocity models were implemented in a QD code and their predictive performance was assessed for a wide range of engine operating conditions. The effects of compression ratio and ignition timing on the in-cylinder combustion were well reproduced irrespective of the employed u l correlation or u te model. However, to predict the effect of changes in mixture composition, the correlation and model selection proved crucial. Compared to existing correlations, a new correlation developed by the current authors led to better reproduction of the effects of equivalence ratio and residual gas content and the combustion duration. For the turbulent burning velocity, the models of Damkohler and Peters consistently underestimated the influence of equivalence ratio and residual gas content on the combustion duration, while the Gulder, Leeds, Zimont and Fractals model corresponded well with the experiments. The combination of one of these models with the new u l correlation can be used with confidence to simulate the performance and efficiency of methanol-fuelled engines.