FUEL AND COMBUSTION
Year:2009 | Volume:1 | Issue:2|Papers Count:5

A numerical simulation of reactive swirling methane/air non-premixed flame in a new three-dimensional model combustion chamber is carried out to assess the performance of two thermal radiation models, namely, the Discrete Transfer Radiation Model and the P-1 Model. A Finite Volume staggered grid approach is employed to solve the governing equations. The second-order upwind scheme is applied for the space derivatives of the advection terms in all transport equations. The SIMPLEC algorithm is used to handle the velocity and pressure coupling. The eddy dissipation model is employed to predict the heat release and the Reynolds stress turbulence model is applied to simulate the flow behavior. A weighted-sum-of-gray-gases model is used for the gas radioactive properties. Computational results with and without the radiation effects are compared with the available experimental data and the two radiation models are evaluated in terms of computational efficiency and prediction accuracy. Comparison of present numerical results with experimental data reveals that the thermal radiation mode is important especially for heat flux on the walls. Both the Discrete Transfer Radiation and P-1 radiation models predict temperature distribution reasonably well, although the latter involves a relatively high computational cost. The P-1 model overestimates heat flux on the walls.

In this paper, the role of reaction mechanism in direct initiation of detonation is studied numerically. The combustion mechanism is presented using a three-step kinetics model, which consists of chain initiation, chain branching and chain termination. In this research, the role of chain initiation on the blast initiation is studied. To investigate the role of chemical mechanism, a characteristic time (t1) is defined for each step, which contains the effect of various kinetics parameters. Numerical simulation shows that extending the initiation characteristic time (t) causes an increase in the critical energy of direct initiation. To demonstrate the role of chain initiation on detonation initiation, shock pressure diagrams are presented for different values of t1, and also for various initiation energies (E0).These diagrams show that for smaller t1’s, kinetics has a more important effect than for larger values of t1’s. Also, it is shown that by increasing the initiation energy, dependence of minimum value of the shock pressure on t1is decreased. For large values of t1’s, the behavior of the wave in the critical initiation is almost independent of t1 thus, detonation behavior for a given Eonearly coincides with the respective t1’s. The relationship between a t1 and Eodepends on the value of t1. For small t1, this relationship is linear with a small slope, whereas for large t1, it is linear with a large slope.

In the present work, the flash points of binary systems (ethanol+n-octane, 1 -propanol+n-octane, 1-propanol+ n-decane, and n-octane+ n-decane) were measured in atmospheric pressure. The resulting flash points data were used in NRTL, Wilson and UNIQUAC models to calculate the mixture binary parameters. The results were subsequently compared with experimentally produced VLE data, and revealed that this method is able to predict the binary interaction parameters of binary mixtures with high accuracy.

This study evaluates the effect of additives on diesel and of additive-ethanol-dieselfuel blends on the density, viscosity, cetane number, flash point, boiling point, distillation and performance in engine tests. An additive is used to keep the blends homogenous and stable, and an ignition improver, which can enhance cetane number in ethanol-diesel fuel blends. The formulations were carried out with 5, 7.5 and 10% v/v of additive ethanol starting from a base diesel. The presence of MXEE (2-Methoxy Ethyl Ether), NM (Nitro Methane), NE (Nitro Ethane) and ethanol in the diesel fuel significantly alters the characteristics of volatility (flashpoint and distillation curve) and increases the cetane number, improving the fuel's performance in engine tests. The performance of the new fuel formulations were studied on a MB-OM 457 LA diesel engine in idle and cut-off speed positions. The results showed that soot formation can be reduced by more than 50%, 30% and 27% with the diesel formulations; E-NE5-10, E-NM5-10 and E-MX5-10, respectively.

Detection of knock onset to control abnormal combustion is one of the most important targets in SI engine modeling. The present contribution describes a refined analytical approach to knock occurrence simulation and its intensity. In the quasi-dimensional model used in this research, the homogeneous charge of the cylinder during the combustion period is assumed to be divided into three parts; these include: burned product, unburned reactant, which comprises the end gas region, and flame front. One of the advantages of this research is its application of turbulent flame propagation to mass burning rate estimation and its use of kinetic reactions mechanism in both burned and unburned zones. A 32 step- and I4 species- mechanism is applied to examine the behavior of the end gas region. Finally, operating parameters, factors affecting knock onset and its intensity (e.g. inlet pressure and temperature, equivalence ratio, spark timing, compression ratio, etc.) have been examined. Moreover, the effects of EGR on knock occurrence and engine output are evaluated as an effective method, and are compared against other factors. The predictive engine model has been validated through comparing the calculated results with the experimental data from an actual engine, and the results show a significant agreement between the two.