Ignition: A Critical First Step For Combustion (original) (raw)
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FUNDAMENTALS OF APPLIED SCIENCE IN COMBUSTION PROCESS OF SPARK IGNITION AUTOMOTIVE (FUEL) ENGINES
This article provides some of the fundamentals applied science to combustion processes in spark ignition engine and take some of the mystery out of making more horsepower with a four stroke engine in a bit to get the most out of the performance engine parts. It went further to examine the basic scientific concepts of volumetric efficiency, thermal efficiency and mechanical efficiency and how they relate to automotive (fuel) engine performance. It found that current work/attention in combustion chemistry is directed towards understanding and predicting the possible impacts of alternative fuels, including fuels derived from biological systems and new geological sources, such as oil shale and oil sands. And to develop knowledge and accelerate the deployment of renewable fuels and new technologies in combustion process in spark ignition engines that increase vehicle efficiency, reduce petroleum consumption, and decrease harmful emissions.
Currently, detailed studies exist on the self-ignition phenomenon in liquid fuels and even for natural gas. However, studies for syngas are quite limited and existing ones are mainly focused on combustion kinetics and do not study self-ignition prior to the ignition point. This paper presents the development of a thermodynamic analysis to study the self-ignition phenomenon in gaseous alternative fuels during the compression stroke in spark-ignited internal combustion engines. Analysis takes into account the fuel composition, relevant process parameters, and variation due to pressure and temperature intake changes. The approach is focused on equilibrium thermodynamics, which easily allows estimating engine operating conditions. These results permit studying adequate compression ratios to obtain good efficiencies, as those achieved by using natural gas, but in heat engine applications to generate power with low-methane-number syngas fuels. Resumen En la actualidad, existen estudios detallados del fenómeno de la auto-detonación en combustibles líquidos e inclusive para el gas natural. Sin embargo, los estudios para gas de síntesis son muy limitados y los existentes se centran principalmente en la cinética de la combustión y no se ha estudiado el autoencendido antes del punto de ignición. En este trabajo se presenta el desarrollo de un análisis termodinámico para estudiar el fenómeno de auto-ignición en combustibles gaseosos alternativos durante la carrera de compresión, cuando son utilizados en motores de encendido provocado. El análisis tiene en cuenta la composición del combustible, los parámetros relevantes del proceso y la influencia debido a los cambios de presión y temperatura en la admisión. El enfoque se centra de la termodinámica de equilibrio, lo que permite una estimación práctica de la condición de funcionamiento del motor. Estos resultados permiten estudiar las relaciones de compresión adecuadas con el fin de obtener eficiencias similares a las obtenidas utilizando gas natural, pero en aplicaciones de motores térmicos para la generación de energía eléctrica utilizando gas de síntesis de metano bajo número como combustible
Kerosene Ignition and Combustion: An experimental and modelling study
The ignition delay time of two JET-A samples obtained at random at two locations (Haifa and Stuttgart) have been investigated in parallel, by two groups of researchers. The experiments carried out in two different shock tube devices covered a temperature range of 1100 to 1900 K at pressures between 2.4 and 6 bar. The four sets of experiments consisting of almost 400 shocks are analyzed, statistically evaluated, and compared with ignition delay experiments for decane. Computer simulation of two surrogate fuel models (i) pure n-decane, (ii) a mixture of 70% n-decane, 30% propylbenzene, are compared to the experimental data. It was found that all measured ignition delay time data can be represented by a single statistical fit. Furthermore, predictions by using pure n-decane as the surrogate fuel match the statistical fit obtained for all the experiments, and explicitly the Stuttgart experiments. A. Introduction Kerosene is the main fuel for all aircrafts, civil and military. Kerosene is a complex fuel containing about 180 individual chemicals. Furthermore, their concentrations and identity change not only according to the source of the fuel, but also according to the refinery where the fuel was distilled. However, in order to cope with the demands of international civil and military aviation, kerosene is the only fuel produced under very strict physical standards defined as Jet-A, Jet A1 and for American Military as JP-4, JP5 etc. (Ranges of boiling point, freezing point, viscosity, polarity, minimum ignition temperature etc. are defined). The chemical composition is not a part of these standards. The physical standards take care of the transport and flow of the jet fuel in the jet aircraft, but the combustion is a function of the chemical components of the fuel. In Fig 1 we present schematically a jet engine combustor. The compressed air at 600 K is flown together with a spray of fuel. The spray vaporizes at very high velocity, within a short time to the gas phase where it is combusted. This information is trivial for aeronautical engineers, but chemists and mechanical engineers have only recently addressed to it [34]. The understanding of how fuels burn and having a computer simulator for the way they release energy is a very important tool in the hands of designers of car and jet engines, rocket engines etc. Without these tools, pollution reduction and increase of efficiencies is problematic. The facts of the real combustion devices are usually not taken into account. Fig 1. Schematic diagram of a jet engine combustion chamber. 400% air flows into the engine at high altitude. The air is compressed aerodynamically by the compressor and its temperature reaches 600 K. 300% of the air flows around the combustion chamber for cooling purposes. Only 100% of the needed air for full combustion of the kerosene enters the combustion chamber at different stages. 12% enter primarily with the fuel spray and causes it to heat and start to evaporate. The droplets travel at high speed and have to fully evaporate before the end of the combustion zone. Droplets that manage to go out of the combustion chamber will hit the turbine and damage it.
This paper talks about combustion efficiency for energy conservation as well as to produce energy in a more environment friendly process by not hampering the operations side.
Effect of Alternative Fuels on the Burning Processes in the Spark Ignition Combustion Engine
Scientific proceedings, 2013
The presented article discusses the use of alternative gaseous fuels (a mixture of natural gas with hydrogen and a mixture of natural gas with carbon dioxide) in spark-ignition engine LGW 702 and their impact on the nature of combustion. An analysis of pressure in the combustion chamber has revealed that increasing volume of hydrogen in the mixture of hydrogen with natural gas leads to shorter ignition delay and shorter overall duration of combustion. On the other hand, increasing proportion of carbon dioxide in the mixture of carbon dioxide with natural gas causes an extension of ignition delay as well as extension of total duration of combustion. The nature of combustion significantly affects the resulting parameters of the combustion engine.
Global reaction mechanism for the auto-ignition of full boiling range gasoline and kerosene fuels
Combustion Theory and Modelling, 2013
Compact reaction schemes capable of predicting auto-ignition are a prerequisite for the development of strategies to control and optimise homogeneous charge compression ignition (HCCI) engines. In particular for full boiling range fuels exhibiting two stage ignition a tremendous demand exists in the engine development community. The present paper therefore meticulously assesses a previous 7-step reaction scheme developed to predict auto-ignition for four hydrocarbon blends and proposes an important extension of the model constant optimisation procedure, allowing for the model to capture not only ignition delays, but also the evolutions of representative intermediates and heat release rates for a variety of full boiling range fuels. Additionally, an extensive validation of the later evolutions by means of various detailed n-heptane reaction mechanisms from literature has been presented; both for perfectly homogeneous, as well as nonpremixed/stratified HCCI conditions. Finally, the models potential to simulate the autoignition of various full boiling range fuels is demonstrated by means of experimental shock tube data for six strongly differing fuels, containing e.g. up to 46.7% cycloalkanes, 20% napthalenes or complex branched aromatics such as methyl-or ethylnapthalene. The good predictive capability observed for each of the validation cases as well as the successful parameterisation for each of the six fuels, indicate that the model could, in principle, be applied to any hydrocarbon fuel, providing suitable adjustments to the model parameters are carried out. Combined with the optimisation strategy presented, the model therefore constitutes a major step towards the inclusion of real fuel kinetics into full scale HCCI engine simulations.
Studies have been carried out on the phenomenon of auto-ignition in liquid fuels and natural gas, but research on the application of gaseous fuels obtained from biomass is limited. Existing investigations about autoignition mainly focused on the combustion kinetics to determine the delay time, but not on the prediction of the set of parameters that encourage the presence of the phenomenon. In the present research, a thermodynamic model is developed for the prediction of the auto-ignition in Spark Ignition Internal Combustion Engine operated with gaseous fuels, which are obtained from the process of gasification of biomass. The formulated model can handle variable compositions of gaseous fuels and to optimize the main operational parameters of the engine, to verify its influence on the phenomenon under study. Results show the application of this type of alternative fuels in commercial engines that operated with natural gas, varying engine operational parameters while maximizing the power output of the engine.