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Research efforts into advanced emission control systems led to significant reduction of pollutant emissions of modern internal combustion engines. Sustainable renewable fuels are used to further reduce their Well-to-Wheels greenhouse gas emissions. The novel aspect of this paper is the compatibility investigation of existing advanced emission control technologies for achieving low pollutant emissions with the use of sustainable renewable fuels with vehicle tests. This is done on a diesel demonstrator vehicle, equipped with Lean NOx trap and dual-SCR technologies in combination with a 48V mild-hybrid powertrain. Tailpipe pollutant and CO2 emissions are measured for market diesel fuel with 7% renewable fatty-acid-methyl-ester (FAME) (B7), diesel fuel with 30% FAME (B30), and 100% renewable hydrotreated vegetable oil (HVO). Results show no significant difference in pollutant emissions between the different fuels used. In a second part of the study, a Well-to-Wheels (WTW) analysis is conducted. This includes different pathways for the biomass-to-liquid fuels that were tested on the vehicle, as well as a power-to-diesel (e-diesel) assessment. Results show that significant WTW CO2 reductions are possibly compared to the state-of-the-art market diesel fuel. Part of this reduction is already possible for the existing fleet as most of paraffinic compounds are drop-in for market diesel fuel.

The European Union (EU) has introduced since the early 1990s a series of progressively more stringent emission regulations to control air pollution from the transport sector, commonly known as Euro standards. Following this path, more recently, with the European Green Deal, the European Commission has indicated the intention to review the current air pollutant emissions standards. This study investigates the emission performance of an advanced demonstrator vehicle developed to meet the increasingly more stringent air pollution limits required. Emissions of currently regulated and unregulated components including NH3, N2O, and SPN10 (solid particle number), were studied in a very wide range of real-world operative conditions. The performance of two new generation portable instruments for the onboard measurement of N2O and NH3 were also evaluated in comparison with reference laboratory equipment. Similarly, the measurement accuracy of onboard NOx sensors was also compared to laboratory reference. The vehicle presented low emissions of NOx and NH3 and relatively low emissions of N2O, also compared to data currently available in the literature, in a broad range of operative conditions, which however resulted in a large variability in emissions.

The heat transfer is a keystone sub-model for engine simulation tools since it affects all targeting parameters (power output, efficiency and emissions. Part I of this work [1] reported a thorough review of heat transfer measurements from literature. Using Design of Experiments (DoE) two measurement matrices were constructed, one for motored and one for fired operation. The present paper focuses on the measurements under fired operation and analyses the heat transfer phenomena in a systematic way. First, the effect of the dependent engine settings on the heat flux is analyzed in a consistent way using ANOVA (Analysis of Variance). Second, it also discusses the influence of the gas properties on the heat flux, which has been overlooked by many authors. Third, the validity of the Reynolds analogy modelling approach is checked, and several improvements are proposed.

The heat transfer from the combustion gases to the cylinder walls inside a spark ignition engine is a key factor in an engine's design, due to its influence on the engine's efficiency, power and emissions. Therefore a lot of research has been conducted in order to accurately model the heat transfer, for engine design and optimization purposes. These models have been found to provide inaccurate predictions for fuels which have significantly different gas properties compared to traditional fossil fuels. This indicates that the models either do not properly include gas properties, or are missing some important properties in their formulation. In order to construct a general (“fuel-independent”) heat transfer model, new measurements need to be executed, with multiple fuels that have different properties. Designing such an experiment requires a thorough understanding of the factors influencing the heat transfer and their interactions. In this paper a literature review is presented of heat transfer measurements in spark ignition engines in order to investigate the effect of the engine factors on the heat transfer. Based on this review, a root cause analysis is conducted to identify the independent factors that affect heat transfer. These factors are then used to set up two experiments according to a Design of Experiments methodology that allows the investigation of the effect of different gas properties and engine settings on the heat transfer in a consistent way. The results of these measurements for motored operation are discussed in [1] and for fired operation in a companion paper [2].

Using light alcohols in spark-ignition engines can improve energy security and offers the prospect of carbon neutral transport. The properties of these fuels enable considerable improvements in engine performance and pollutant emissions. Whereas most experimental studies have focused on ethanol, this paper provides experimental results gathered on various methanol-fuelled engines. A comparison against gasoline on two flex-fuel engines yielded relative efficiency benefits of about 10% for methanol thanks to more isochoric combustion, less pumping, cooling and dissociation losses. Lower combustion temperatures allowed to reduce engine-out NO x by 5–10 g/kWh. The CO 2 values dropped by more than 10%. Alternative load control strategies, employing mixture richness or exhaust gas recirculation (EGR) to control load while keeping the throttle wide open, were compared on a single cylinder engine. The EGR strategy seems preferable as it allows to increase part load efficiency up to 5% without sacrificing in terms of tailpipe emissions. Finally, this load control strategy of choice was applied to a turbocharged, high compression ratio engine to demonstrate that methanol can be used in dedicated engines with diesel-like efficiencies (up to 42%) and emission levels comparable to or lower than gasoline 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. © 2013 Springer-Verlag Berlin Heidelberg.

In the current work, the variation of EGR rates is investigated in a hydrogen-fueled, spark-ignition engine. This technique is followed in order to control the engine load and decrease the exhaust nitrogen oxides emissions. The external EGR is varied in the very wide range of 12% up to 47% (by mass), where in each test case the in-cylinder mixture is stoichiometric, diluted with the appropriate EGR rate. The operation of this engine is explored using measured data with the aid of a validated CFD code. Moreover, a new residual gas term existing in the expression of the hydrogen laminar flame speed, which has been derived from a one-dimensional chemical kinetics code, is tested in a real application for appraising its capabilities. The investigation conducted provides insight on the performance and indicated efficiency of the engine, the combustion processes, and the emissions of nitrogen oxides. More precisely, an experimental study has been deployed with the aim to identify the characteristics of such a technique, using very high EGR rates, focusing on the combustion phenomena. At the same time, the CFD results are compared with the corresponding measured ones, in order to evaluate the CFD code under such non-conventional operating conditions and to test a recent expression for the residual gas term included in the hydrogen laminar flame speed expression. It is revealed that the combustion takes place in few degrees of crank angle, especially at high engine loads (low EGR rates), whereas the exhaust nitrogen oxides emissions are significantly decreased in comparison to the use of lean mixtures for controlling the engine load. Additionally, the recent expression of the residual gas term, which has been tested and incorporated in the CFD code, seems to be adequate for the calculation of combustion phenomena in highly diluted, with EGR, hydrogen-fueled spark-ignition engines, as for every EGR rate tested (even for the higher ones) the computational results are compared in good terms with the measured data.

Understanding the heat transfer mechanism from the combustion gases to the walls inside an internal combustion engine is key in the search for higher efficiencies, higher power outputs and lower emissions. Current heat transfer modeling concepts have been reported to be inaccurate for hydrogen engines. To investigate the heat transfer mechanisms in a hydrogen engine, we have measured the instantaneous heat loss inside a spark-ignition engine at three locations. To determine the effect of the throttle position, compression ratio, ignition timing and air-to-fuel ratio in the entire parameter space systematically, techniques of Design of Experiments are applied. The experiment has been repeated for methane, gasoline and methanol to compare hydrogen with other fuels and to build a database for the development of a fuel independent heat transfer model. The paper shows that the effect of the engine factors is similar for all the fuels. However, the heat loss to the cylinder walls of hydrogen is only at the same level of that of the other fuels for very lean mixtures. The engine efficiency drastically reduces for rich mixtures as a consequence, indicating that a lean mixture in combination with boosting and external gas recirculation should be used to obtain high power outputs with high efficiencies for port fuel injected engines.

Hydrogen-fuelled internal combustion engines are being 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 would enable a cheap and fast optimization of engine settings for operation on hydrogen, facilitating the development of these engines. The accuracy of the heat transfer submodel 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 heat transfer models in engine research are those from Annand and Woschni. These models are developed for fossil fuels, which have different combustion properties. Therefore, they need to be evaluated for hydrogen. We have measured the heat flux and the wall temperature in an engine that can run on hydrogen and methane. This paper describes an evaluation of the models of Annand and Woschni, using those heat flux measurements and assesses if the models capture the effect of changing combustion and fuel properties. The models fail on all the tests, so they need to be improved to accurately model the heat transfer generated by hydrogen combustion.

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.

Hydrogen-fuelled internal combustion engines are an attractive alternative to current drive trains, because a high efficiency is possible throughout the load range and only emissions of oxides of nitrogen (NOx) can be emitted. The latter is an important constraint for power and efficiency optimization. Optimizing the engine with experiments is time consuming, so thermodynamic models of the engine cycle are being developed to speed up this process. Such a model has to accurately predict the heat transfer in the engine, because it affects all optimization targets. The standard heat transfer models (Annand and Woschni) have already been cited to be inaccurate for hydrogen engines. However, little work has been devoted to the evaluation of the flow-field based heat transfer model, which is the topic of this paper. The model is evaluated with measurements that focus on the effect of the fuel, under motored and fired operation. The experiments were designed with DoE techniques to systematically investigate the effects over the entire parameter space. The results demonstrate that the flow-field based heat transfer model is better able to capture the effect of changing in-cylinder gas properties under motored operation compared to the model of Woschni. However, it is not accurate during combustion either, so model improvements are required to increase the modeling accuracy. Copyright © 2013 SAE International.

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.

In louvered fin heat exchangers, the flow deflection influences the heat transfer rate and pressure drop and thus the heat exchanger’s 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 (intertube 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.

Past investigations have shown that the current type-approval test cycles are not representative for real-world vehicle usage. Consequently, the emissions and fuel consumption of the vehicles are underestimated. Therefore, a new cycle is being developed in the UNECE framework (World-harmonised Light-duty Test Procedure, WLTP), aiming at a more dynamic and worldwide harmonised test cycle. To provide recommendations for the new cycle, we have analysed the noxious emission results of a test programme of seven vehicles on the test cycles NEDC (New European Driving Cycle) and CADC (Common Artemis Driving Cycles). This paper presents the results of that analysis to show the zones of the cycle that are causing the highest emissions, using two different approaches. Both approaches show that the zones with the highest emissions of modern vehicles differ from vehicle to vehicle. Consequently, a representative test cycle has to contain as many combinations of vehicle speed and acceleration that occur in real-world traffic as possible to prevent that a vehicle does not perform well for certain combinations because they are not included in the test cycle. Furthermore, the paper demonstrates that it is important to include a cold start to ensure rapid warm up of the catalysts.

The use of biomass-derived ethanol in spark-ignition engines is an interesting option 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 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 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 mechanisms 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-fueled spark-ignition engines, are presented. These correlations can now be implemented in an engine code.

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/n-heptane 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.

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. Copyright © 2012 SAE International.

The use of hydrogen derived methanol in spark-ignition engines forms a promising approach to decarbonizing transport and securing domestic energy supply. Methanol can be renewably produced from hydrogen in combination with biomass or CO2 from the atmosphere and flue gases. From well to tank studies it appears that hydrogen derived methanol compares favourably with liquid or compressed hydrogen both in terms of production cost and energy efficiency. Since existing well to wheel studies are based on outdated technology, this paper tries to provide efficiency figures for state-of-the-art hydrogen and methanol engines using published data and measurements on our own flex-fuel engine. Both fuels offer a great potential for efficiency improvements compared to gasoline engines thanks to a variety of favourable properties. However, there is a clear distinction between engines specifically designed for hydrogen or methanol operation and flex-fuel engines, which should also run on gasoline. For dedicated engines, the literature indicates that peak brake thermal efficiencies up to 45% and 42% are possible on hydrogen and methanol respectively. The ability to employ qualitative load control instead of throttling enables relative efficiency improvements compared to gasoline between 10 and 20% due to reduced pumping losses in part load. On our flex-fuel engine, operation on hydrogen using qualitative load control enabled the highest efficiencies, especially at low loads, where improvements up to 40% relative to gasoline were possible. At elevated loads, rising NOx emissions necessitated a switch to throttled stoichiometric operation, resulting in efficiencies comparable to those on gasoline. The efficiency benefit of methanol is more modest (5–10% relative to gasoline), but can be retained over the entire load range. These improvements are mostly due to reduced pumping losses, increased burning velocities and a slight decrease in cooling losses. Future well-to-wheel studies should take this considerable potential for efficiency improvements into consideration and should also distinguish between dedicated and flex-fuel engines.

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.

International audience; Hydrogen-fuelled internal combustion engines are a possible solution to make transportation more ecological. Only emissions of oxides of nitrogen (NOx) occur at high loads, being a constraint for power and effciency optimization. A thermodynamic model of the engine cycle enables a cheap and fast optimization of engine settings.It needs to accurately predict the heat transfer in the engine because the NOx emissions are influenced by the maximum gas temperature. However, The existing engine heat transfer models in the literature are developed for fossil fuels and they have been cited to be inaccurate for hydrogen. We have measured the heat transfer inside a spark ignited engine with a thermopile to investigate the heat transfer process of hydrogen and to find the differences with a fossil fuel. This paper describes the effects of the compression ratio, ignition timing and mixture richness on the heat transfer process, comparing hydrogen with methane. A convection coeffcient is used to separate the effect of the temperature difference between the gas and the wall from the influence of the gas movement and combustion. The paper shows that the convection coeffcient gives more insight in the heat transfer process in a combustion engine despite the assumptions involved in its definition. The comparison between hydrogen and methane demonstrates, in contrast to what is believed, that the heat loss of hydrogen can be lower.

This work concerns the study of a spark-ignition engine fueled with hydrogen, using both measured and numerical data at various conditions, focusing on the combustion efficiency, the heat transfer phenomena and heat loss to the cylinder walls, the performance, as well as the nitric oxide (NO) emissions formed, when the fuel/air and compression ratio are varied. For the investigation of the heat transfer mechanism, the local wall temperatures and heat flux rates were measured at three locations of the cylinder liner in a CFR engine. These fluxes can provide a reliable estimation of the total heat loss through the cylinder walls and of the hydrogen flame arrival at specific locations. Together with the experimental analysis, the numerical results obtained from a validated in-house CFD code were utilized for gaining a more complete view of the heat transfer mechanism and the hydrogen combustion efficiency for the various cases examined. The performance of the CFR engine is then identified, since the calculated cylinder pressures are compared with the measured ones, from which performance and heat release rates are calculated and discussed. Further, NO emission studies have been accomplished, with the calculated results not only being compared with the measured exhaust NO ones, but also further processed for conducting an in-depth investigation of the dependence of NO production on the spatial distribution of in-cylinder gas temperature. It is revealed that for lower fuel/air ratio the burned gas temperature is held at low level and the heat loss ratio is quite low. As the load increases and stoichiometric mixtures are used, the wall and in-cylinder gas temperatures increase substantially, together with the heat loss and the NO emissions, owing to the high hydrogen combustion velocity and the consequent high rate of temperature rise. The combustion efficiency is slightly increased, but the indicated efficiency is decreased due to higher heat loss.

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.

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.

Hydrogen-fueled internal combustion engines are a possible solution to make transportation more ecological. Apart from difficulties in production and storage of hydrogen, there are three major bottlenecks in the operation of hydrogen-powered engines: reaching a high power output, reducing NOx emissions at high loads and avoiding backfire. This paper presents an experimental study of the influence of continuously variable valve timing of the intake valves on these bottlenecks. Measurements were performed on a four-cylinder engine that can run on gasoline as well as on hydrogen. The measurements on hydrogen are compared to those on gasoline. For hydrogen, the effects of the cam phasing were investigated at wide open throttle, where load is controlled by the quality of the mixture (equivalence ratio) as well as in throttled mode, where load is defined by the quantity of mixture. Results show that it is possible to optimize the applied control strategy by using variable valve timing as a means to increase the range of both the qualitative and quantitative load control methods, which contributes to an easier switch between both methods.

This paper describes an experimental investigation of heat transfer inside a CFR spark ignition engine operated at a constant engine speed of 600 rpm. The heat flux is directly measured under motored and fired conditions with a commercially available thermopile sensor. The heat transfer during hydrogen and methane combustion is compared examining the effects of the compression ratio, ignition timing and mixture richness. Less cyclic and spatial variation in the heat flux traces are observed when burning hydrogen, which can be correlated to the faster burn rate. The peak heat flux increases with the compression ratio, but the total cycle heat loss can decrease due to less heat transfer at the end of the expansion stroke. An advanced spark timing and increased mixture richness cause 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.