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Technical Paper

The Effects of Charge Non-Uniformity on Autoignition in a Gas Fuelled Motored Engine

The effects of charge non-uniformity on autoignition of methane/air mixtures in a motored engine are investigated analytically using a varying global kinetic data model derived from the results of a detailed chemical kinetic scheme under similar conditions in a simple adiabatic constant volume reactor. These derived varying global kinetic data model was implemented in the CFD KIVA-3 code. The relative contribution of fluid motion generated by piston motion, heat transfer, chemical reactivity of the cylinder charge and swirl movement to the inhomogeneities in the properties of the cylinder charge and their consequent effects on the evolution of the autoignition process are presented and discussed.
Technical Paper

Examination of Operational Limits in Gas Fueled Spark Ignition Engines

There are distinct operational mixture limits beyond which satisfactory spark ignition engine performance can not be maintained. The values of these limit mixtures which depend on the mode of their determination, are affected by numerous operational and design factors that include the type of engine and fuel used. Simple approximate methods are presented for predicting these limits. Good agreement is shown to exist between the calculated and the corresponding experimental values over a range of operating conditions while operating on the gaseous fuels: methane, propane and hydrogen. The experimentally observed operational limits deviate very substantially from the corresponding accepted flammability limit values for quiescent conditions evaluated at the average temperature and pressure prevailing at the instant of the spark passage.
Technical Paper

An Investigation of the Effects of the Addition of Dissociated Water Products to a Gas Fueled Spark Ignition Engine

One of the main features of methane fueled spark ignition engines is their relatively slow flame propagation rates in comparison to liquid fuel applications which may lead to relatively lower power output and efficiency with increased emissions and cyclic variations. This is especially pronounced at operational equivalence ratios that are much leaner than the stoichiometric value. The addition of some hydrogen and oxygen to the methane may contribute towards speeding the combustion process and bring about significant improvements in performance and emissions. It has been suggested that the addition to the methane of products of water electrolysis generated in situ on board of a vehicle may produce such improvements.
Technical Paper

An Examination of the Combustion Processes of a Methane Fuelled Engine When Employing Plasma Jet Ignition

Examination is made of the changes that take place in the major parameters of the combustion process and engine performance when using three different designs of plasma jet igniters of the open cavity type in a methane fuelled single cylinder engine. The characteristics of the combustion process were analysed employing a two-zone diagnostic model based on cylinder pressure-time development data. The use of plasma jet igniters with methane as a fuel enhanced the rates of burning in the initial stages of combustion, especially with very lean mixtures. The lean limit of engine operation was also extended. Their use for near stoichiometric fast burning mixtures tends in comparison to contribute little towards enhancing engine performance.
Technical Paper

Knock and Combustion Characteristics of CH4, CO, H2 and Their Binary Mixtures

Hydrogen is normally produced through the steam reforming of fossil fuels, notably natural gas or their partial oxidation in oxygenated air. The products of these processes would normally produce the H2 in the presence of a variety of concentrations of CO, CO2, H2O and N2. There is increasing interest in employing such mixtures whether on their own or in mixtures with traditional liquid or gaseous fuels in S.I. engine applications so as to improve the combustion process and engine performance. The combustion characteristics in S.I. engines of gas mixtures that contain H2 and CO need to be established to provide key operational information, such as the variations in the combustion duration and the knock limits. This paper presents experimental data obtained in a single cylinder, variable compression ratio, S.I., CFR engine when operated in turn on CH4, H2, CO and their binary mixtures.
Technical Paper

The Combustion of Gaseous Fuels in a Dual Fuel Engine of the Compression Ignition Type with Particular Reference to Cold Intake Temperature Conditions

The present contribution is mainly concerned with an investigation of the characteristics of dual fuel operation under cold intake temperatures, primarily from the viewpoint of engine performance and exhaust emissions. The gaseous fuels employed were methane, propane, hydrogen and ethylene. The addition of the inerts carbon dioxide and nitrogen were also considered. Comparison with the corresponding normal diesel operation was made throughout.
Technical Paper

The Dual Fuel Engine of the Compression Ignition Type - Prospects, Problems and Solutions - A Review

A review is made of some of the main problems associated with the use of natural gas, notably methane, in dual fuel engines of the compression ignition diesel type. It is shown that such applications represent in principle a very attractive mode for the utilization of the fuel for the production of power generally at relatively high efficiencies and outputs with good exhaust emissions characteristics. Some relevant solutions to the problems outlined are then discussed. Moreover, some further research and development needed in this general area is also outlined.
Technical Paper

Comparative Studies of Methane and Propane as Fuels for Spark Ignition and Compression Ignition Engines

The paper reviews the combustion characteristics of the two fuels and sets out to consider their respective performance in both spark ignition and compression ignition engines. Results of comparative tests involving spark ignition engines over a wide range of operating conditions are presented and discussed. Some of the performance characteristics considered are those relating to power output, efficiency, tendency to knock, cyclic variations, optimum spark requirements and exhaust emissions. Similarly, some of the performance characteristics in compression ignition engines considered include power output, efficiency, tendency towards knock and autoignition, exhaust emissions and low operational temperature problems. Finally, the relative operational safety aspects of the two fuels are evaluated. It is then suggested that in this regard, methane has some excellent physical, chemical and combustion characteristics that makes it a particularly safe fuel.
Technical Paper

Hydrogen as a Fuel and the Feasibility of a Hydrogen-Oxygen Engine

A preliminary investigation was made into the use of hydrogen-oxygen mixtures in spark ignition engines. This appeared to be attractive in view of the serious air pollution problem. Furthermore, hydrogen has been considered by others as a possible alternative fuel to replace depleting petroleum resources. Following a literature survey regarding the combustion characteristics of hydrogen, a computer program based on a constant-volume combustion engine cycle was used to evaluate the overall performance of an engine. Another program, which considered chemical reaction kinetics, was used to predict the onset of autoignition in mixtures undergoing compression in an engine. Results of the program indicated that an attractive and safe way to use hydrogen-oxygen mixtures in an engine involved the recycling of exhaust gases. Such a system would be fed with a stoichiometric mixture, while excess hydrogen would be circulated within to control combustion in the engine.
Technical Paper

The Effects of Low Ambient Temperatures on the Combustion of Natural Gas in a Single-Cylinder Spark Ignition Engine

Operating characteristics including ignition limits, cyclic variability, and exhaust emissions were studied in the combustion of natural gas in a spark ignition, single-cylinder, variable compression ratio engine, operated at intake mixture temperatures ranging between 120 and -60 F. The work confirmed in general the feasibility of using natural gas in a spark ignition engine operated under extremely cold intake temperature conditions. It was learned that both the maximum peak cylinder pressures and the mass of mixture inducted by the engine increased as the intake mixture temperature was lowered, and that the emissions of pollutants were not significantly increased. These findings are thought to be particularly relevant to the use of natural gas in spark ignition engines, either as LNG or under very cold wintry conditions.
Technical Paper

The Ignition of a Premixed Fuel and Air Charge by Pilot Fuel Spray Injection with Reference to Dual-Fuel Combustion

Dual fuel engines compress the air/gas fuel mixture to just below autoignition conditions and then ignite it by the injection of a small amount of liquid fuel. The use and performance of these engines, however, have been limited by knock. Single cylinder engine experiments show that this limitation is a readily defined autoignition phenomenon, and can be analyzed by a mathematical model that indicates the effects on performance imposed by fuel changes and operating conditions. Experimental findings confirm that these performance data correlate broadly with those obtained conventionally in standard spark ignited or motored engines.
Technical Paper

Some Considerations of Cyclic Variations in Spark Ignition Engines Fuelled with Gaseous Fuels

Cyclic variations in engines have been the subject of much investigation and there are some excellent reviews of this research. However, there is still a need to examine in an integrated manner the cyclic variation in performance parameters such as indicated power output, efficiency and cylinder pressure development in relation to the cyclic variation in some important combustion parameters notably those of the ignition lag, which is the time requirements to initiate a flame kernel following the passage of a spark and the duration to complete the combustion process particularly when gaseous fuels, notably methane are used. The paper describes the results of an investigation with these objectives using a single cylinder, variable compression ratio, spark ignition, CFR engine, run at constant speed, operating mainly on natural gas.
Technical Paper

Gross Chemical Kinetics from Motored Piston Engines

The paper describes the computational and experimental approach of deriving gross chemical kinetic data of the combustion of common fuels using a motored engine. The approach is based on the accurate calculation of the rate of heat release due to autoignition reactions. Kinetic data of the combustion of n-heptane, propane, and methane in air together with the role of the presence of a higher hydrocarbon vapour such as n-heptane with methane and propane are presented and discussed mainly in relation to dual-fuel engine phenomena.
Technical Paper

Some Considerations of the Safety of Methane, (CNG), as an Automotive Fuel - Comparison with Gasoline, Propane and Hydrogen Operation

The total number of vehicles fuelled with compressed natural gas, CNG, is relatively very small in comparison to gasoline fuelled vehicles. Accordingly, because of the lack of statistics of accidents involving CNG fuelled vehicles, their safety aspects are evaluated in comparison to automobiles fuelled with gasoline or some other alternative fuels such as propane, hydrogen, LNG or LH2. It is suggested that methane, CNG, has some excellent physical, chemical and combustion characteristics that make it a safe automotive fuel. These characteristics are reviewed and the superior relative safety of methane in automotive applications in comparison to applications involving the other fuels is demonstrated where well designed conversion systems and operations are employed.
Technical Paper

A Predictive Model for Knock in Spark Ignition Engines

The present contribution combines the consideration of the chemical reaction activity of the end gas and engine operating conditions to predict the onset of knock and associated performance in a spark ignition engine fuelled with methane. A two-zone predictive combustion model was developed based on an estimate of the effective duration of the combustion period and the mass burning rate for any set of operating conditions. The unburned end gas preignition chemical reaction activity is described by a detailed chemical reaction kinetic scheme for methane and air. The variation with time of the value of a formulated dimensionless knock parameter based on the value of the cumulative energy released due to preignition reaction activity of the end gas per unit volume relative to the total energy release per unit cylinder swept volume is calculated It is shown that whenever knocking is encountered, the value of builds up to a sufficiently high value that exceeds a critical value.
Technical Paper

A Predictive Model for Knock in Dual Fuel Engines

A model is described for the prediction of the onset of autoignition and knock in compression ignition engines of the dual fuel type. The associated variations with time of performance parameters such as the energy release rate, cylinder pressure and charge temperature, power output and species concentrations can also be obtained. This is achieved through modelling in detail the chemical reaction rates of the gaseous fuel during compression and subsequently during diesel fuel pilot ignition and combustion. A comprehensive reaction scheme involving 105 reaction steps with 31 chemical species is employed for the purpose. The results are based mainly on methane or propane as the gaseous fuel while accounting for the contribution of pilot diesel fuel injection. Calculated data showed good general agreement with the corresponding experimental values.
Technical Paper

Methane-Carbon Dioxide Mixtures as a Fuel

The presence of carbon dioxide with methane is often encountered to varying proportions in numerous natural, industrial and bio-gases. The paper discusses how such a presence modifies significantly the thermodynamic, kinetic and combustion characteristics of methane in air. Experimental results are presented showing how the performance of engines, both of the spark ignition and compression ignition dual fuel types is adversely affected by the increasing presence of carbon dioxide with the methane. The bases for these trends are discussed and some guidelines towards alleviating the adverse effects of the presence of carbon dioxide in such fuel mixtures are made.
Technical Paper

A Predictive Model for the Combustion Process in Dual Fuel Engines

A multi-zone model has been developed for the prediction of the combustion processes in dual fuel engines and some of their performance features. The consequences of the interaction between the gaseous and the diesel fuels and the resulting modification to the combustion processes are considered. A reacting zone has been incorporated in the model to describe the partial oxidation of the gaseous fuel-air mixture while detailed kinetic schemes are employed to describe the oxidation of the gaseous fuel, right from the start of compression to the end of the expansion process. The associated formation and concentrations of exhaust emissions are correspondingly established. The model can predict the onset of knock as well as the operating features and emissions for the more demanding case of light load performance. Predicted values for methane operation show good agreement with corresponding experimental values.
Technical Paper

The Effects of Pilot Fuel Quality on Dual Fuel Engine Ignition Delay

The effects of changes in the cetane number of diesel liquid pilot fuels on the ignition delay period in dual fuel engines were investigated experimentally. Different pilot fuel quantities were employed with commercially pure methane, propane and low heating value gaseous fuel mixtures of methane with nitrogen or carbon dioxide over a range of engine load. The ignition delay variation with increased gaseous fuel admission showed a strong dependance on both the quantity and the quality of the pilot fuel used. It was found that the use of high cetane number pilot liquid fuels permitted smaller pilot quantities to be used satisfactorily. Engine operation on propane and low heating value gaseous fuels improved in comparison with dual fuel engine operation employing common diesel fuels.
Technical Paper

An Analytical Approach for the Optimization of a SI Engine Performance Including the Consideration of Knock

The present contribution describes an analytical approach for predicting the highest limit for acceptable power or efficiency for any spark ignition engine while ensuring knock free operation. A deterministic gradient based model combined with a simple genetic algorithm were used in association with a two-zone engine combustion model to predict analytically the necessary changes in specified operating parameters to produce optimum performance. Various examples involving mainly spark ignition engine operation with methane-hydrogen fuel mixtures are presented and discussed.