The Period of Ignition Delay for Methane-Air Mixture with Hydrogen and Ethylene Additives

The article is devoted to estimating the intensifying efficiency of methane-air ignition by adding a small amount of hydrogen and/or ethylene. It presents features of the experimental determination of the ignition delay period for fuel-air mixtures using shock installation and methods of processing empirical data. The testing of the known ignition kinetic models for methane, hydrogen, and ethylene with air was carried out. The results of test calculations were compared with those previously published, as well as original experiments. The kinetic model was chosen to provide the minimum discrepancy between the calculated and experimental data. The regularities of the effect of hydrogen and ethylene additives on the ignition dynamics of the methane-air mixture for the range of initial pressures from 1 to 8 bar at temperatures from 900 to 1100 K were obtained with the use of non-stationary numerical modeling. Methane-air mixtures with the mass fraction of additives not exceeding 10% were studied. The quantitative indicators of possible reduction in the ignition delay period of methane-air mixtures were detected.

Study on Diesel Low-Nitrogen or Nitrogen-Free Combustion Performance in Constant Volume Combustion Vessels and Contributory

This paper studies the combustion performance of diesel in constant volume combustion vessels under different conditions of mixed low-nitrogen (O2 and N2) or non-nitrogen (O2 and CO2) in varying proportions. The high-speed camera is used to shoot the combustion flame in the constant volume combustion vessel. The process and morphology of the combustion flame are amplified in both time and space to study and analyze the effects of different compositions and concentrations in gases on the combustion performance of diesel and conduct a study on the contributory factors in the performance of diesel with no nitrogen. According to the study, in the condition of low nitrogen, the O2 concentration is more than 60%, the ignition delay period is shortened, the combustion flame is bright and slender, it spreads quickly, and the blue flame appears when the O2 concentration reaches 70%; While for nitrogen-free combustion, only when the O2 concentration reaches 30% is the combustion close to the air condition; when the O2 concentration reaches 40%, the combustion condition is optimized obviously and the combustion flame is relatively slender compared to the air working condition. Similarly, with the increase of the O2 concentration, the ignition delay period of nitrogen-free diesel is shortened, the duration is extended, and the combustion performance is optimized. In addition, when the O2 concentration reaches 50%, with the decrease of the initial temperature, the ignition delay period is prolonged, and the duration is shortened obviously. When the temperature is lower than 700 K, there is no ignition. The increase of the diesel injection pressure is beneficial to optimize the ignition performance of diesel non-nitrogen combustion and shorten its ignition delay period and combustion duration. Related research has important guiding significance to optimize nitrogen-free combustion technology, which produces no NOx of the diesel engine.

Simulation Study of Ignition Characteristics of Impinging Sprays in Constant Volume Chamber

The present study involves the simulation of a constant volume, non-premixed, hot surface spray combustion of diesel fuel for a given set of injection pressure, compressed air pressure (cylinder air pressure) and hot surface temperature (hot plate temperature) and their effects on ignition delay period. Fuel injection pressure was varied from 100 bar – 300 bar in steps of 100 bar, cylinder air pressure in the range of 20 bar to 40 bar (in steps of 10 bar) and hot surface temperature from 623 K to 723 K (50 K steps). The problem was solved using 2D axisymmetric geometry. A structured mesh of about 1.24 lac nodal points was created and tested for grid independency. For solving flow behavior, a pressure solver was used with a turbulence model of k-ε with enhanced wall functions. While a volumetric eddy dissipation model was used to solve combustion phenomena. Ignition delay period was calculated with the help of static temperature versus time plot. It is found that keeping any two operating parameters constant, third operating parameter is inversely proportional to ignition delay period. The results of the present simulation study are in a fairly good agreement with the experimental studies at same operating conditions.

Homogeneous Ignition Delay, Flame Propagation Rate and End-Gas Autoignition Fraction Measurements of Natural Gas and Exhaust Gas Recirculation Blends in a Rapid Compression Machine

To evaluate the effect of exhaust gas recirculation (EGR) and variable fuel reactivity on knock and misfire in spark ignited national gas engines, experiments were conducted in a rapid compression machine to measure homogeneous ignition delay, flame propagation rate, and end-gas autoignition fraction for stoichiometric natural gas/oxidizer/EGR blends. Natural gas with a range of chemical reactivity was simulated using mixtures of CH4, C2H6, and C3H8. Reactive exhaust gas recirculation (R-EGR) gases were simulated with mixtures of Ar, CO2, CO, and NO and non-reactive exhaust gas recirculation gases (NR-EGR) were simulated with mixtures of AR and CO2. Homogeneous ignition delay period, flame propagation rate and end-gas autoignition fraction were measured at compressed pressures and temperatures of 30.2 to 34.0 bar and 667 to 980 K, respectively. Flame propagation rate decreased with both R-EGR and NR-EGR substitution. The substitution of R-EGR increased the end-gas autoignition fraction, whereas NR-EGR substitution decreased the end-gas autoignition fraction. The results indicate that the presence of the reactive species NO in the R-EGR has a strong impact on end-gas autoignition fraction. An 82-species reduced chemical kinetic mechanism was also developed that reproduces measured homogeneous ignition delay period with a total average relative error of 11.0%.

Experimental investigations to predict optimistic biodiesel(s) and its optimistic operating conditions by varying ignition delay period and fuel spray pressures for lower emissions and better performance

In this study, different characteristics of sustainable renewable biodiesels (those have a high potential of their production worldwide and in India) were compared with the characteristics of neat diesel to determine optimistic biodiesel for the diesel engine at 250 bar spray pressure. Optimistic fuel gives a comparatively lower level of emissions and better performance than other selected fuels in the study. Rubber seed oil methyl ester was investigated as an optimistic fuel among the other selected fuels such as sunflower oil methyl ester, neem seed oil methyl ester, and neat diesel. To enhance the performance characteristics and to further decrease the level of emission characteristics of fuel ROME, further experiments were conducted at higher spray (injection) pressures of 500 bar, 625 bar, and 750 bar with varying ignition delay period via varying its spray timings such as 8°, 13°, 18°, 23°, 28°, and 33° before top dead center. Spray pressure 250 bar at 23° before top dead center was investigated as an optimistic operating condition where fuel rubber seed oil methyl ester gives negligible hydrocarbon emissions (0.019 g/kW h) while its nitrogen oxide (NOX) emissions were about 70% lesser than those observed with neat diesel, respectively.

Features of the Piston Engine Working Process when Working on Kerosene

For aircraft in light multi-purpose aviation, piston engines are considered more efficient than gas turbine. The main technical requirement for such engines is to ensure trouble-free operation with the best possible fuel efficiency. At the same time, there are no requirements to emission of harmful substances in exhaust fumes except for the absence of visible smoke. When developing multi-purpose aircraft piston engines, it is important to ensure their multi-fuel operation, including opera-tion on TS-1 kerosene and diesel fuel. But the issues associated with setting engine control algo-rithms for operation on TS-1 kerosene are practically unexplored. In order to refine the control algo-rithms, the flow of the working process using such fuel was studied in this work. The effect of se-quencing the working process stages on the formation of the ignition delay period was shown. Based on the analysis of the factors affecting the ignition delay period, a map of the fuel injection advance angle values was generated. According to the experimental data, the activation energy of pre-flame reactions was adopted, which for kerosene TS-1 was 23–28 kJ/mol.