Practical fuels are a complex mixture of thousands of hydrocarbon compounds, making it challenging and difficult to study their combustion behavior. It's generally agreed that in order to study these complex practical fuels a much simpler approach of studying simple fuel surrogates containing limited number of components is more feasible. Ethanol and n-heptane have been studied as primary reference fuels in the surrogate study of gasoline and diesel over the past few decades. The objective of the following thesis has been to study the autoignition characteristics of ethanol and n-heptane and validate chemical kinetic mechanisms. The validation of a chemical kinetic mechanism provides a deeper insight into the combustion behavior of the fuels which can be further used to study advanced combustion concepts. Experiments have been conducted on the rapid compression machine (RCM) and validated against mechanisms from literature study. Rapid compression machines have been primarily used to study chemical kinetics at low to intermediate temperatures and high pressures for their accuracy and reproducibility. For the following study experiments span over a range of temperature (650-1000 K), pressure (10, 15 and 20 bar) and equivalence ratio ([phi]=0.3, 0.5, 1). Experimental data based on the adiabatic volumetric expansion approach have been modeled numerically using the Sandia SENKIN code in conjunction with CHEMKIN. Experiments have been primarily focused on validating kinetic mechanisms at low to intermediate temperatures and elevated pressures. Ignition delay time data from experiments have been deduced based on the pressure and time histories. A brute sensitivity and flux analysis has been performed to reveal the key sensitive reactions and the dominant reaction pathways followed under the present experimental conditions. Improvements have been suggested and discrepancies noted in order to develop a valid chemical kinetic mechanism. Under the present experimental conditions for the study of ethanol, reactions involving hydroperoxyl radicals, namely C2H5OH+HȮ2 and CH3CHO+ HȮ2 as well as the formation of H2O2 from HȮ2 radical and its subsequent decomposition have been found to be sensitive. Based on the following, improvements and developements have been suggested to increase the accuracy and predictability of the mechanisms studied. Ignition delay data from experiments have been compared against those obtained from the mechanism used in the study for n-heptane. Discrepancies have been found in the low temperature region, with the mechanism under predicting the first ignition delay. The causes for the discrepancy have been noted to be due to the NTC behaviour exhibited during the two stage ignition of n-heptane. At low temperatures the reaction pathway proceeded by chain branching mainly due to the ketohydroperoxide species reaction pathway has been analysed. As the temperature of the reaction increases the reaction pathway is dominated by the ȮOH species propagation resulting in the formation of conjugate olefins and [Beta]-decomposition products, a further investigation of which can help improve the predictability of the mechanism.

As it becomes more and more difficult to find "easy" oil, various alternative fuels are introduced to the markets. These fuels have chemical properties that are different from the traditional gasoline and diesel fuels so that engine efficiency and other engine behaviors may be affected To improve engine efficiency and to identify which alternative fuel is the cleanest fuel solution, it is necessary to compile information about the ignition delay, which governs auto-ignition in spark-ignition (SI), compression-ignition (CI) and homogeneous charge compression-ignition (HCCI) engines. In this study, we measured ignition delay on the Rapid Compression Machine (RCM). RCM is a single-stroke device, which compresses uniform mixtures to engine-like condition. We can interpret from the pressure the detailed heat release process. A comprehensive ignition delay database of toluene/n-heptane mixtures and gasoline/ethanol mixtures was established The data allow us to calculate the auto-ignition behavior in engines. Depending on application the correct choice of alternative fuels may be made.

A computer model is used to examine oxidation of hydrocarbon fuels in a rapid compression machine. For one of the fuels studied, n-heptane, significant fuel consumption is computed to take place during the compression stroke under some operating conditions, while for the less reactive n-pentane, no appreciable fuel consumption occurs until after the end of compression. The third fuel studied, a 60 PRF mixture of iso-octane and n-heptane, exhibits behavior that is intermediate between that of n-heptane and n-pentane. The model results indicate that computational studies of rapid compression machine ignition must consider fuel reaction during compression in order to achieve satisfactory agreement between computed and experimental results.

Previously we have reported on the combustion behavior of all nine isomers of heptane in a rapid compression machine (RCM) with stoichiometric fuel and ''air'' mixtures at a compressed gas pressure of 15 atm. The dependence of autoignition delay times on molecular structure was illustrated. Here, we report some additional experimental work that was performed in order to address unusual results regarding significant differences in the ignition delay times recorded at the same fuel and oxygen composition, but with different fractions of nitrogen and argon diluent gases. Moreover, we have begun to simulate these experiments with detailed chemical kinetic mechanisms. These mechanisms are based on previous studies of other alkane molecules, in particular, n-heptane and iso-octane. We have focused our attention on n-heptane in order to systematically redevelop the chemistry and thermochemistry for this C-- isomer with the intention of extending our greater knowledge gained to the other eight isomers. The addition of new reaction types, that were not included previously, has had a significant impact on the simulations, particularly at low temperatures.

Homogeneous charge compression ignition (HCCI)/controlled auto-ignition (CAI) has emerged as one of the most promising engine technologies with the potential to combine fuel efficiency and improved emissions performance, offering reduced nitrous oxides and particulate matter alongside efficiency comparable with modern diesel engines. Despite the considerable advantages, its operational range is rather limited and controlling the combustion (timing of ignition and rate of energy release) is still an area of on-going research. Commercial applications are, however, close to reality.HCCI and CAI engines for the automotive industry presents the state-of-the-art in research and development on an international basis, as a one-stop reference work. The background to the development of HCCI / CAI engine technology is described. Basic principles, the technologies and their potential applications, strengths and weaknesses, as well as likely future trends and sources of further information are reviewed in the areas of gasoline HCCI / CAI engines; diesel HCCI engines; HCCI / CAI engines with alternative fuels; and advanced modelling and experimental techniques. The book provides an invaluable source of information for scientific researchers, R&D engineers and managers in the automotive engineering industry worldwide. - Presents the state-of-the-art in research and development on an international basis - An invaluable source of information for scientific researchers, R&D engineers and managers in the automotive engineering industry worldwide - Looks at one of the most promising engine technologies around