Homogeneous-charge Engine Research Articles

Large-eddy simulations of a stratified-charge direct-injection spark-ignition engine: Comparison with experiment and analysis of cycle-to-cycle variations

Multiple-cycle large-eddy simulations (LES) have been performed for an optically accessible, single-cylinder, four-stroke-cycle, spray-guided direct-injection spark-ignition (SG-DISI) engine operating in a stratified globally fuel-lean mode. The simulations combine a standard Smagorinsky turbulence model, a stochastic Lagrangian parcel method for liquid fuel injection and fuel spray modeling, a simple energy-deposition spark-ignition model, and a modified thickened flame model for turbulent flame propagation through highly stratified reactant mixtures. Comparisons between simulations and experiments include individual-cycle and ensemble-average pressure and apparent-heat-release-rate traces, individual-cycle and ensemble-average indicated mean effective pressures (IMEP), and instantaneous two-dimensional vapor-equivalence-ratio contours. Although the number of LES cycles is small (35), the results show that the simulations are able to capture the global combustion behavior that is observed in the experiments, including cycle-to-cycle variations. The simulation results are then analyzed further to provide insight into the conditions that lead to misfire versus robust combustion. As has been reported in earlier experimental and LES studies for homogeneous-charge SI engines, local conditions in the vicinity of the spark gap at the time of ignition largely determine the subsequent flame development. However, in contrast to homogeneous-charge engines, no single local or global quantity correlates as strongly with the eventual peak pressure or IMEP for each cycle. Rather, it is the interplay among the early flame kernel, the velocity field that it experiences, and the fuel distribution that it encounters that ultimately determines the fate of each combustion event. Deeper analysis and quantitative statistical comparisons between experiments and simulations will require the simulation of larger numbers of engine cycles.

Experimental investigation of effect of stratified charging system adopted to gasoline engine running with LPG on engine performance

The energy conversation and values of limited emission level are very important issue for manufacturers and engine designers. Therefore the investigations about homogeneous charge engine and stratified charge (SC) engine have commonly been considered by the literatures. Homogeneous charge engines run with stoichiometric mixture, and SC engines run with lean mixture. The main purpose of this study, in order to run with poor mixture of gasoline engine like diesel engine, the shape of charge was converted to SC and used liquid petroleum gases (LPG) fuel. In this point of view, LPG–air mixture is prepared in two different environments and rates, and the mixture was taken into the engine as stratified by two steps. The effects of engine performance, fuel consumption and emission characteristics are investigated for SC application. The experiments were made under full load and full throttle position. According to the results of the experiments, both the engine power and torque did not change and the fuel consum...

Unsteady wall heat flux in spark-ignited, homogeneous charge engines fuelled with reformer gas/gasoline blends

On-board partial oxidation of gasoline to produce reformer gas seems to be an attractive strategy to abate pollutant emissions from internal combustion engines. The engine behaviour in terms of efficiency and combustion process can be better understood by means of in-cylinder heat flux measurements. The study of the unsteady wall heat transfer, supported by previous studies of flame propagation and flame speed through ion sensors and optical fibres, reveals a limited influence of the reformer gas upon the heat transfer coefficient and possibly upon the flame-quenching distance, which is estimated in three different and independent ways. A detailed statistical analysis of single-cycle heat flux shows that the cycle-to-cycle variation remains large when the fraction of reformer gas in the fuel blend increases, even if the global engine stability improves. The comparison of numerous data shows how the chemical energy is released partly within the flame and partly within the post-flame region. This last can account for as much as 30 per cent of the total energy release. The analysis of slow and fast-burning cycles with different fuel blends shows that this fraction of energy is released only when, during the expansion stroke, the cylinder temperature decreases below a certain threshold, allowing radicals to recombine and carbon monoxide (CO) completely to oxidize to CO 2.

On unsteady premixed turbulent burning velocity prediction in internal combustion engines

In this work, it is shown how to extend the turbulent burning velocity approximation by Peters [N. Peters, Turbulent Combustion, Cambridge University Press, 2000.] for premixed flames in the flamelet regime in order to account for instationary turbulent flame development. Such instationary flame development occurs in spark ignition engines. The burning velocity approximation is embedded into the level set concept [F.A. Williams, in: J. Buckmaster (Ed.), The Mathematics of Combustion, SIAM, Philadelphia, 1985, pp. 97–131; N. Peters, J. Fluid Mech. 384 (1999) 107–132.] for premixed flames that distinguishes between large scale and small scale turbulence. Based on that formulation, a spark ignition criterion for successful ignition of premixed flames is presented. This criterion is based on the competition of premixed turbulent flame propagation and global curvature effects. The turbulent flame brush thickness is employed as a measure for the evolution of the flame. The combustion model is validated against homogeneous charge engine experiments. The results show that initial flame propagation is well predicted, which indicates that the unsteady evolution of the premixed flame is well captured.

Not Even the Kitchen Sink

This article focuses on the increasing commercial application of capillary force vaporization. Possibilities range from fuel oil burners to the sophisticated kerosene heaters that are popular in Japan. A new stove will introduce capillary force vaporizing as a way of atomizing fuel, stepping away from cartridge and metal-tank stoves that dominate the market. Researchers in the United States are also exploring the technology’s suitability to diesel and homogeneous charge compression (HCCI) ignition and engines. A capillary force vaporizer’s ability to vaporize low-volatility diesel fuel at atmospheric temperatures and pressures gives the technology an edge over air-assist or other methods that produce small droplets. A capillary force vaporizer could be applied to a Heel engine in the manifold between turbocharger and intake valves or a vaporizer could be installed in the combustion chamber itself. Jetboil Inc. of Guild, N.H., integrated a pot, burner, heat exchanger, canister, and insulator into a single unit to promote efficient fuel use. As a result, the stove uses less fuel in the field, which is about half that of a conventional pot-and-stove setup that lacks an engineered interface.

Stretch in Premixed Laminar Flames Under IC Engine Conditions

Flamelet models for turbulent combustion provide an approach (via the laminar flame) to include detailed flame chemistry into fluid dynamic simulations of IC engines. The flamelet model postulates that a turbulent flame is a statistical distribution of premixed, laminar flames. However. turbulence affects the laminar flames through strain (a) and curvature. The effect of positive strains (outflow condition) on counter-flow flames is evaluated by integrating the species destruction (or formation) through the flame.This integral is the net reaction per area of the flame and is compared to the integral for the unstrained flame. Strain reduces the net reaction rate per unit area. Flame stretch is a measure of the reduction in fuel consumption due to turbulent strain. Flame stretch is a property tending to slow turbulent flame speeds by the reduction in fuel consumption. In a strained flame, reactant and product reaction rates are changed by different amounts indicating that the internal structure of the flame is affected by strain. Analysis of engine conditions suggests that the average strain varies from 1000-120,000sec-1 dependent on rpm and intake produced turbulence. A strained laminar flame with a = 50,000sec= under conditions typical of a motored engine at TDC loses 50% of the net formation rate of CO2 compared to the unstrained flame. This flame can tolerate strains over a range of engine conditions, but not without distortion. Reducing φ to 0.6 drastically decreases the tolerance of the flame to strain. The effects of strain on these flames due to cylinder residuals and EGR have not yet been evaluated. This analysis of strain from engine turbulence on a laminar flame suggests that flame stretch should be included in turbulent combustion models in homogeneous charge engines.

A turbulent-combustion model for homogeneous charge engines

A turbulent combustion model suitable for multidimensional, homogeneous charge engine calculation was developed. The model is based on the laminar flamelet assumption suggested in the literature for premixed combustion. Unlike previous approaches using this assumption and the variance of a progress variable to estimate the probability of flame occurrence, the new model uses both the laminar flame structure and the relevant turbulence parameters to calculate the dissipation rate of the fluctuating component of the progress variable. This is shown to yield plausible dependence of the turbulent flame speed on the laminar flame speed and on the mixture turbulence. Preliminary testing of the model was made by comparison with engine data. The computed results were in good qualitative agreement with the experimental results, but some quantitative discrepancies were observed. There are several possible causes for the observed discrepancies. One of the most likely causes is the cyclic variability present in the data, which is not accounted for in the model.

Fuels for Aircraft Engines

It is unnecessary to enlarge on the importance of the fuels used in aviation in a paper before this Society. Not only is fuel quality the most important individual factor to be considered in the economics of civil aviation, but engine development, aircraft design and performance depend upon it.An apology is offered, in view of the title of the paper, that as it is barely possible in the confines of a single paper to deal adequately with the volatile fuels (known as petrols and gasolines) used in the normal carburettor or homogeneous charge engines, other types of fuels have necessarily been omitted.