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A rapid compression machine for chemical kinetic studies has been developed. The design objectives of the machine were to obtain: 1)uniform well-defined core gas; 2) laminar flow condition; 3) maximum ratio of cooling to compression time; 4) side wall vortex containment; and, 5) minimum mechanical vibration. A piston crevice volume was incorporated to achieve the side wall vortex containment. Tests with inert gases showed the post-compression pressure matched with the calculated laminar pressure indicating that the machine achieved these design objectives. Measurements of ignition delays for homogeneous PRF/O2/N2/Ar mixture in the rapid compression machine have been made with five primary reference fuels (ON 100, 90, 75, 50, and 0) at an equivalence ratio of 1, a diluent (s)/oxygen ratio of 3.77, and two initial pressures of 500 Torr and 1000 Torr. Post-compression temperatures were varied by blending Ar and N2 in different ratios.

Flame propagation at elevated pressures for propane, butane and autogas (20% propane and 80% butane by mass) were investigated. Flame arrival time was measured using ionization probes installed along the wall of a cylindrical combustion chamber. Flame radius was also measured using a laser schlieren technique. Results showed that the flame front speed decreased with increasing initial pressure, and the initial pressure effect on maximum flame front speed was correlated by the relationship Sf = 175·pi-0.15 (for Φ=1.0). Characteristics of flame front speed between propane, butane and autogas were very similar, whereas at fuel-rich conditions flame front speed of butane and autogas were higher than that of propane. A thermodynamic model to predict flame radius and speed as a function of time was derived and tested using measured pressure-time curves.

The combustion mechanism of a fuel droplet cloud was studied by numerical simulation. We investigated how the flame front speed and combustion products changed depending on the equivalence ratio and initial temperature. Modeling was performed using the KIVA-III software package, a three dimensional analysis software used mainly for internal combustion engine applications. The computational domain was a horizontal 1x1x100 cell sector of a spherical combustion chamber and the fuel was n-decane. Results showed that when all the fuel droplets were assumed to have evaporated, the flame front speed increased from 28 cm/s to 152 cm/s as the equivalence ratio increased. The maximum flame front speed was reached at ϕ=1.1, beyond which it decreased (at richer overall equivalence ratios). With a constant equivalence ratio, the flame front speed decreased near the outside region, because the unburned gas was compressed by the expanding burned gas.

An LPG engine for heavy duty vehicles has been developed using liquid phase LPG injection (hereafter LPLI) system, which has regarded as as one of next generation LPG fuel supply systems. In this work the optimized piston cavities were investigated and chosen for an LPLI engine system. While the mass production of piston cavities is considered, three piston cavities were tested: Dog-dish type, bathtub type and top-land-cut bathtub type. From the experiments the bathtub type showed the extension of lean limit while achieving the stable combustion, compared to the dog-dish type at the same injection timing. Throughout CFD analysis, it was revealed that the extension of lean limit was due to an increase of turbulence intensity by the enlarged crevice area, and the enlargement of flame front surface owing to the shape of the bathtub piston cavity compared to that of the dog-dish type.

The prediction of knock onset in spark-ignition engines requires a chemical model for the autoignition of the hydrocarbon fuel-air mixture, and a description of the unburned end-gas thermal state. Previous studies have shown that a reduced chemistry model developed by Keck et al. adequately predicts the initiation of autoignition. However, the combined effects of heat transfer and compression on the state of the end gas have not been thoroughly investigated. The importance of end-gas heat transfer was studied with the objective of improving the ability of our knock model to predict knock onset over a wide range of engine conditions. This was achieved through changing the thermal environment of the end gas by either varying the inlet air temperature or the coolant temperature. Results show that there is significant heating of the in-cylinder charge during intake and a substantial part of the compression process.

The autoignition characteristics of methanol, ethanol and MTBE (methyl tert-butyl ether) have been investigated in a rapid compression machine at pressures in the range 20-40 atm and temperatures within 750-1000 K. All three oxygenated fuels tested show higher autoignition temperatures than paraffins, a trend consistent with the high octane number of these fuels. The autoignition delay time for methanol was slightly lower than predicted values using reported reaction mechanisms. However, the experimental and measured values for the activation energy are in very good agreement around 44 kcal/mol. The measured activation energy for ethanol autoignition is in good agreement with previous shock tube results (31 kcal/mol), although ignition times predicted by the shock tube correlation are a factor of three lower than the measured values. The measured activation energy for MTBE, 41.4 kcal/mol, was significantly higher than the value previously observed in shock tubes (28.1 kcal/mol).

An aerodynamic model of the entrainment of the head wall quench layer during blowdown and exhaust of an internal combustion engine has been developed. The model may be used to calculate the time resolved concentration and mass flowrate of hydrocarbons (HC) in the exhaust, from a knowledge of engine geometry and operating conditions. It predicts that the area As from which HC are swept will be proportional to the cube root of the ratio of the quench layer thickness δq to the thickness of the viscous boundary layer δv. Since the mass of HC emitted is proportional to the product of the HC density ρHC, the area As and the thickness δq, the HC emissions will be proportional to the product ρHC δq4/3 and this is the most important factor determining the emissions.

Experiments by Gatowski and Heywood have been analyzed to obtain both qualitative and quantitative information on early flame development and burning rates in a square piston premixed spark-ignition engine. Flame growth was observed using high speed Schlieren photography and simultaneous pressure records were obtained using piezo-electric transducers. To study the effects of in-cylinder gas motion several combinations of shrouded and unshrouded inlet valves, and flat and stepped pistons were used. Spark position was also varied. The analysis supports the wrinkled laminar flame model of turbulent flame structure in spark-ignition engines. It also suggests that cycle-by-cycle variations in the growth rate and location of the flame kernel at very early times are the major cause of cycle-by-cycle pressure variations in spark-ignition engines.

This is a preliminary work for the development of a stratified combustion engine using liquefied petroleum gas(LPG) as an alternative fuel. The main objective of this research is to find out the optimizing engine parameters from the viewpoint of mixture formation with the aid of simulation, where the KIVA_ code was used. The combustion characteristics of LPG and gasoline are different because of their different physical properties. Therefore, the numerical simulation was performed for optimizing engine parameters by changing the piston and cylinder geometry, as well as injection conditions. Result showed that geometry of combustion chamber has a great influence on mixture stratification. Also, weaker swirl seems to be better for mixture formation in the vicinity of the spark plug.

Using an extended bottom view piston having a quartz window, flame propagation observation and flame contour analysis were carried out to investigate the combustion characteristics of a heavy-duty type LPG lean burn engine. The swirl ratio and piston cavity configuration were varied to investigate their effects on combustion and engine performance. Gradual reduction of NOx but increased hydrocarbon emissions were measured for leaner mixtures compared to the stoichiometric operation. High swirl apparently accelerated the initial flame kernel development, as evidenced by a shorter crank angle interval from the spark ignition to the maximum cylinder pressure. The ‘D’ type cavity, with an increased squish area located below the intake valve, was shown to have the shortest burn duration among the piston cavities tested. The experimental flame propagation observation procedure was shown to be useful for the study of the combustion process in engines.

A model for describing turbulent flame propagation in internal combustion engines is presented. The model is based upon the assumption that eddies having a characteristic radius ℓe are entrained by the flame front at a turbulent entrainment velocity ue and subsequently burn in a characteristic time τ = ℓe/uℓ, where uℓ is the laminar flame speed for the fuel-air mixture. An approximate analytic method for determining the equilibrium state of the burned gases is also presented. To verify the predictions of the model, experiments were carried out in a single-cylinder research engine at speeds from 1000-3200 rpm, spark advances from 30-110 deg btc and fuel-air equivalence ratios from 0.7-1.5. Simultaneous measurements of the cylinder pressure and the position of the flame front as a function of crank angle were made, and good agreement with the predictions of the model was obtained for all operating conditions.