Sebastian Verhelst

Hydrogen engine-specific properties

Abstract Hydrogen is seen as one of the important energy vectors of the next century. Hydrogen as an energy carrier, provides the potential for a sustainable development particularly in the transportation sector. A hydrogen fueled engine has the potential for substantially cleaner emissions than other internal combustion engines. Other benefits arise from the wide flammability limits and the high flame propagation speed, both allowing better efficiency. The Laboratory of Transporttechnology (University of Ghent) converted a GM/Crusader V8 SI engine for hydrogen use, to be built in a city bus. A sequential timed multipoint injection system was implemented. Attention is directed towards special characteristics related to the use of hydrogen as a fuel in IC engines: ignition properties (smaller spark plug gap), injection pressure (dependent on the means of storage: compressed gas or liquid), quality of the lubricating oil (due to higher blow-by volumes, a substantial amount of hydrogen is present in the crankcase), oxygen sensors (very lean operating conditions). The advantages and disadvantages of a power regulation by changing the air to fuel ratio (as for diesel engines), as compared to throttle regulation (SI engines) are judged.

Aspects concerning the optimisation of a hydrogen fueled engine

Abstract Hydrogen fueled engines are known for several advantages, among which is the very low concentration of pollutants in the exhaust gases compared to internal combustion engines using traditional or other alternative fuels. Hydrogen driven vehicles thus reduce both local as well as global emissions. Furthermore, because of the wide flammability limits and the high flame propagation speed of hydrogen, a hydrogen fueled engine is capable of very lean combustion, allowing power regulation by varying the richness of the air–fuel mixture. Thus, better efficiency is reached because of the possibility to work without throttle valves. The Laboratory of Transport Technology (Ghent University) converted a GM/Crusader V8 SI engine for hydrogen use. A sequential timed multipoint injection system was implemented. The corresponding electronic management system was used to optimise the engine parameters (ignition timing, injection timing and duration) and to program several corrections in the case of changing working conditions (fuel pressure and temperature, inlet combustion air pressure and temperature, etc.). Finally, the goal of the development is discussed: the building-in of the engine in a city bus, with its conditions of sufficient power ( 90 kW ) and torque output ( 300 N m ), together with extreme low emission levels and backfire-safe operation.

Influence of the injection parameters on the efficiency and power output of a hydrogen fueled engine

The advantages of hydrogen fueled internal combustion engines are well known, certainly concerning the ultra-low noxious emissions (only NO x is to be considered). Disadvantages are the backfire phenomenon and the gaseous state of hydrogen at atmospheric conditions. A complete control of the mixture formation is necessary and therefore a test engine with sequential port injection was chosen. The tests are carried out on a single-cylinder CFR engine with the intention to use the results to optimize a 6 and 8-cylinder engine with multipoint injection. Different positions of the injector against the intake air duct are examined (represented as different junctions). A numerical simulation CFD code (FLUENT) is used under stationary conditions (continuous injection) for all geometries and under real conditions (sequential injection) for one situation. For each of the geometries the influences of the start of injection, the air/fuel equivalence ratio, injection pressure, and ignition timing on the power output and efficiency of the engine are analyzed. A comparison and discussion is given for all results. It is clearly shown that the start of injection for a certain engine speed and inlet geometry influences the volumetric efficiency and thus the power output of the engine due to the interaction between the injected hydrogen and the inlet pressure waves. Furthermore, the small influence of the injection pressure and the contradictory benefits of the different junctions between power output and fuel efficiency are measured. With retarded injection, so that cool air decreases the temperature of the hot-spots in the combustion chamber before the fuel is injected, backfire safe operation is possible.

Experimental Study of a Hydrogen-Fueled Engine

The Laboratory of Transport Technology (Ghent University) converted a GM/Crusader V-8 engine for hydrogen use. The engine is intended for the propulsion of a midsize hydrogen city bus for public demonstration. For a complete control of the combustion process and to increase the resistance to backfire (explosion of the air-fuel mixture in the intake manifold), a sequential timed multipoint injection of hydrogen and an electronic management system is chosen. The results as a function of the engine parameters (ignition timing, injection timing and duration, injection pressure) are given. Special focus is given to topics related to the use of hydrogen as a fuel: ignition characteristics (importance of electrode distance), quality of the lubricating oil (crankcase gases with high contents of hydrogen), oxygen sensors (very lean operating conditions), and noise reduction (configuration and length of intake pipes). The advantages and disadvantages of a power regulation only by the air-to-fuel ratio (as for diesel engines) against a throttle regulation (normal gasoline or gas regulation) are examined. Finally, the goals of the development of the engine are reached: power output of 90 kW, torque of 300 Nm, extremely low emission levels, and backfire-safe operation.

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.

The Chemical Route to a Carbon Dioxide Neutral World

Excessive CO2 emissions in the atmosphere from anthropogenic activity can be divided into point sources and diffuse sources. The capture of CO2 from flue gases of large industrial installations and its conversion into fuels and chemicals with fast catalytic processes seems technically possible. Some emerging technologies are already being demonstrated on an industrial scale. Others are still being tested on a laboratory or pilot scale. These emerging chemical technologies can be implemented in a time window ranging from 5 to 20 years. The massive amounts of energy needed for capturing processes and the conversion of CO2 should come from low-carbon energy sources, such as tidal, geothermal, and nuclear energy, but also, mainly, from the sun. Synthetic methane gas that can be formed from CO2 and hydrogen gas is an attractive renewable energy carrier with an existing distribution system. Methanol offers advantages as a liquid fuel and is also a building block for the chemical industry. CO2 emissions from diffuse sources is a difficult problem to solve, particularly for CO2 emissions from road, water, and air transport, but steady progress in the development of technology for capturing CO2 from air is being made. It is impossible to ban carbon from the entire energy supply of mankind with the current technological knowledge, but a transition to a mixed carbon-hydrogen economy can reduce net CO2 emissions and ultimately lead to a CO2 -neutral world.

A comprehensive overview of hydrogen engine design features

Abstract Realizing decreased CO2 emissions from the transport sector will be possible in the near future when substituting (part of) the currently used hydrocarbon-fuelled internal combustion engines (ICEs) with hydrogen-fuelled ICEs. Hydrogen-fuelled ICEs have advanced to such a stage that, from the engine point of view, there are no major obstacles to doing this. The present paper indicates the advantages of hydrogen as a fuel for spark ignition (SI) internal combustion engines. It also shows how the hydrogen engine has matured. An extensive overview is given of the literature on experimental studies of abnormal combustion phenomena, mixture formation techniques, and load control strategies for hydrogen-fuelled engines. The Transport Technology research group of the Department of Flow, Heat and Combustion Mechanics at Ghent University has been working on the development and optimization of hydrogen engines for 15 years. An overview of the most important experimental results is presented with special focus on the most recent findings. The article concludes with a list of engine design features of dedicated hydrogen SI engines.

A laminar burning velocity correlation for hydrogen/air mixtures valid at spark-ignition engine conditions

During the development of a quasi-dimensional simulation programme for the combustion of hydrogen in spark-ignition engines, the lack of a suitable laminar flame speed formula for hydrogen/air mixtures became apparent. A literature survey shows that none of the existing correlations covers the entire temperature, pressure and mixture composition range as encountered in spark-ignition engines. Moreover, there is ambiguity concerning the pressure dependence of the laminar burning velocity of hydrogen/air mixtures. Finally, no data exists on the influence of residual gases. This paper looks at several reaction mechanisms found in the literature for the kinetics of hydrogen/oxygen mixtures, after which one is selected that corresponds best with available experimental data. An extensive set of simulations with a one-dimensional chemical kinetics code is performed to calculate the laminar flame speed of hydrogen/air mixtures, in a wide range of mixture compositions and initial pressures and temperatures. The use of a chemical kinetics code permits the calculation of any desired set of conditions and enables the estimation of interactions, e.g. between pressure and temperature effects. Finally, a laminar burning velocity correlation is presented, valid for air-to-fuel equivalence ratios λ between 1 and 3 (fuel-to-air equivalence ratio 0.33 < φ < 1), initial pressures between 1 bar and 16 bar, initial temperatures between 300 K and 800 K and residual gas fractions up to 30 vol%. These conditions are sufficient to cover the entire operating range of hydrogen fuelled spark-ignition engines.Copyright

Characterization of Jatropha curcas oils and their derived fatty acid ethyl esters obtained from two different plantations in Cuba.

The scope of this work is to evaluate some properties of the oils and derived fatty acid ethyl esters (FAEE) from two different Jatropha Curcas species planted in Cuba. The properties that were determined include the acid value, peroxide value, p-anisidine value and fatty acid ethyl esters composition. In order to study the influence of the genus species and geographic conditions on the fuel properties, the oils from Jatropha Curcas planted in two regions of Cuba and their derived FAEE were analyzed and compared. The two plantations were in San Jose (SJ) and Guantanamo (Gt) representing respectively the western and eastern part of the island. The analyses indicated that the FAEE obtained from Guantanamo has a higher acid value and peroxide value compared with the FAEE from San Jose. The p-anisidine values did not show a clear trend and the results of gas chromatography-mass spectrometry indicated a similar FAEE composition. The results obtained by gas chromatography are in good agreements with previous reports

Assessment of Empirical Heat Transfer Models for a CFR Engine Operated in HCCI Mode

Homogeneous charge compression ignition (HCCI) engines are a promising alternative to traditional spark- and compression-ignition engines, due to their high thermal efficiency and near-zero emissions of NOx and soot. Simulation software is an essential tool in the development and optimization of these engines. The heat transfer submodel used in simulation software has a large influence on the accuracy of the simulation results, due to its significant effect on the combustion. In this work several empirical heat transfer models are assessed on their ability to accurately predict the heat flux in a CFR engine during HCCI operation. Models are investigated that are developed for traditional spark- and compression-ignition engines such as those from Annand [1], Woschni [2] and Hohenberg [3] and also models developed for HCCI engines such as those from Chang et al. [4] and Hensel et al. [5]. The heat flux is measured in a CFR engine operated in both motored and HCCI mode and compared to the predicted heat flux by the aforementioned models. It is shown that these models are unable to accurately predict the heat flux during HCCI operation if the model coefficients are not properly calibrated. The models from Annand, Hohenberg and Woschni overestimate the heat flux, whereas the models from Chang et al. and Hensel et al. underestimate it during the entire engine cycle if the original model coefficients are used. If the model coefficients are properly calibrated, the models from Annand, Hohenberg and Hensel et al. are able to predict the heat flux during HCCI operation for one engine operating point. However, if the same model coefficients are used for another operating point, the models are unable to satisfactorily predict the heat flux.