The paper presents results of experimental studies on the methane and propane ignition process in various volumetric compositions of oxidizers heated to temperatures higher than ignition point of analyzed fuels (HTAC conditions–High Temperature Air Combustion conditions). The increment of temperature DT and the ignition delay time tig are parameters characterizing the process of ignition under these conditions. These parameters are functions of equivalence ratio j, temperature of the oxidizer Toxi and the volumetric composition of oxidizer zi. In order to achieve the minimum ignition delay time tig and the maximum increment of the temperature DT, the oxidizer temperature didn’t have to be maximized.There is an interval of Toxi in which analyzed the parameters reaching their extreme values.

A new reliable simple model is presented for estimating the AUTOIGNITION temperatures (AITs) of different classes of hydrocarbons including alkanes, alkenes, cycloalkanes, cycloalkenes, alkynes, and aromatics. For various categories of hydrocarbons with general formula Ca1Ha2, the new correlation can be expressed as: AIT=647+33.33a1 −20.79a2 +58.20F SH+81.03F BH where two functions F SH and F BH are related to size and branches of different classes of hydrocarbons, respectively. The proposed simple model can predict the AIT of any complex hydrocarbons through the knowledge of their molecular structures. The novel correlation is derived and tested for a large number of hydrocarbons including 274-compound database, which is the largest dataset with respect to previous works. It is shown that the estimated results of the new method have a lower root mean square deviation of AIT as compared to three of the best available predictive methods.

Sponge iron (DRI) due to the high surface area, often shows a high tendency to re-oxidation and at some cases spontaneous combustion (AUTOIGNITION). In this work, re-oxidation behavior and AUTOIGNITION of sponge iron, produced from different types of iron ore has been investigated. Isothermal and non-isothermal re-oxidation, experiments were carried out on each type of DRI and their AUTOIGNITION, temperature was determined. Microscopic examination and porosimetric measurements also were used to elucidate the relationship between the DRI specification and its re-oxidation behavior. The type and chemical analysis of the iron ore, used for the production of DRI, had a strong influence on the microstructure of sponge iron and, in turn, on its sensitivity to re-oxidation and AUTOIGNITION.

In this study, the effect of additives such as ammonium oxalate (AO), mixture of ammonium oxalate and strontium carbonate (SC) on AP/HTPB based composite propellants was investigated by burning rate, DTA, density and AUTOIGNITION temperature measurements. The results show that the burning rates of these propellants are decreased significantly. DTA and AUTOIGNITION temperature experiments results indicate respectively that the decomposition and AUTOIGNITION temperatures of AP with these additives are increased. The burning rate temperature sensitivity of AP/HTPB based propellants is reduced significantly by the addition of AO or AO/SC, but the effect of AO is less than that of AO/SC. The reduced heat released at the burning surface of AP/HTPB/AO is responsible for the reduced temperature sensitivity. Synergetic effect between AO and SC at AP/HTPB/SC/AO based propellants causes the reduction of heat release and augmentation of the burning surface temperature. Thus, the burning rate temperature sensitivity is reduced. The results of this research in comparison with other results showed that the temperature sensitivity of the propellant formulation with 4% AO was lowered up to 4.8%.

In this paper, a turbulent lifted diffusion jet flame is studied using the composition probability density function approach in a two-domensional domain with detailed chemistry. The main purpose is to investigate the effect of density variations on scalar fields and lift-off height. For this purpose, the standard k-e model as well as a modified turbulence model for variable density conditions are employed to investigate the impact of turbulence models on the flame behavior and the place of stabilization. The results show that the best agreement between the numerical results and measurements is achieved using the modified turbulence model. A comparison between the numerical results and measurements shows that the standard k-e model over-predicts the spreading and decay rates in the jet. Using the velocity-pressure gradient term in the modified turbulence model resolves the relevant problem to a great extent and leads to better results than those of the standard k-e model.

The objective of this paper is to present a simulation model for controlling combustion phasing in order to avoid knock in turbocharged SI engines. An empirically based knock integral model was integrated in a quasi-dimensional simulation tool. The empirical knock model was optimized and validated against engine tests. This model can be used to optimize control strategy of combustion initiation in SI engine to reach the maximum berak turque. The model is able to predict knock onset with an accuracy of 2 crank angle degrees. With the established knock model, it is possible not only to investigate whether knock is observed by changing operating and design parameters, but also to evaluate their effects on knock intensity.

In this paper, the performance of a natural gas HCCI engine is studied through a thermodynamic model including detailed chemical kinetics. It is shown that as hydroxyl radical has important effects on natural gas combustion, it is possible to quantify SOC with hydroxyl concentration variations. Meanwhile the in-fluence of using formaldehyde as an additive on the engine characteristics has been investigated. Results show that it is possible to change the engine working limits using this additive. Lower AUTOIGNITION tem-perature of formaldehyde causes advanced combustion in natural gas HCCI engine. In TIVC = 410K case, adding 5% formaldehyde would lead to more than 10 CA advance in SOC. Furthermore, there is an opti-mum additive content for each operating condition, which leads to higher output work and power. It is also shown that the air/fuel mixture will ignite earlier using this additive so it is conceivable to reduce inlet mixture temperature resulting in better performance due to higher volumetric efficiency.

The ducted fuel injection strategy is a method that significantly reduces soot emissions in direct injection compression ignition engines. Fuel is injected into the combustion chamber through a duct enhancing the air-fuel mixture. It guarantees more efficient combustion and less soot formation by reducing the equivalence ratio at the AUTOIGNITION zone inside the combustion chamber. The effects of the duct fuel injection on the performance, combustion, and emission of the compression ignition engine were numerically investigated in this study. The duct geometries with varying diameters, lengths, and stand-off distances were examined to find the most appropriate size using an experimentally validated CFD model and detailed soot model. Results show that up to 66. 7% reduction in soot emissions were observed with the usage of the ducted fuel injection strategy compared to conventional diesel combustion. In addition to reducing soot emissions, the ducted fuel injection strategy decreased CO and HC emissions by 20. 4% and 7. 8%, respectively. While the ducted fuel injection strategy reduces emissions, it does not decrease engine performance, on the contrary, it increases gross IMEP by 0. 58%.

Homogeneous charge compression ignition (HCCI) is regarded as the next generation combustion trend in terms of high thermal efficiency and low emissions. It is difficult to control AUTOIGNITION and combustion because they are controlled primarily by the chemical kinetics of air/fuel mixture. In this study, a homogeneous mixture of natural- gas and air was used in a compression ignition engine to reduce NOx emissions and improve thermal efficiency. In order to control ignition timing and combustion, a small amount of Dimethyl Ether (DME) was mixed with the natural-gas. In this paper, a multi- dimensional computational fluid dynamics (CFD) model coupled with chemical kinetics mechanisms was applied to investigate the effects of various temperatures, pressures, equivalence ratios and fuel compositions on the combustion performance and emission characteristics of an HCCI engine. The mixture could run the engine quietly and smoothly over a wide range of loads. Under the present test conditions, finite amount of DME was necessary in order to achieve ignition of the mixture. In addition, thermal efficiency was higher than that of methane fueled engine, when the DME proportion was optimized. NOx emissions were extremely low, however, the emissions of total unburned hydrocarbon were high.

A method is presented to predict the onset of knock and associated performance of a spark ignition engine when primarily fuelled with gaseous fuels such as methane. It gives guidelines for choosing the best operating conditions to obtain maximum power just before the onset of knock. 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. The variation with time of the value of a formulated dimensionless knock parameter K is calculated. This parameter relates the total energy released within the end gas due to AUTOIGNITION reaction activity per unit of corresponding instantaneous volume relative to total energy release per cylinder volume that would take place normally due to regular flame propagation. When knocking is encountered, the value of K builds up to a sufficiently high value that exceeds an acceptable limit. Under normal operating conditions, the value remains throughout the combustion period at comparatively low levels.