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Flame propagation characteristics, in a heavy-duty type LPG lean burn SI engine, were investigated by simulation methodology, using the global one step and the ten step chemical kinetic reaction mechanisms, respectively. The swirl ratio and equivalence ratio were varied to investigate their effects on flame front speed. The effect of increased swirl intensity on flame speed was very minor at ranges of equivalence ratio of this study. Flame front shape, however, was affected by swirl intensity. Circular flame front formed for a higher swirl ratio, which is in a qualitative accordance with that of measurements. Comparison between calculation and measurements of flame propagation characteristics shows a good agreement for both the global one step and the ten step chemical kinetic model. This work concludes that the reduced chemical kinetic reactions, consisting of ten steps, is useful for flame propagation study in an LPG SI engine.

Band spectrum images for CH, OH and CHO were taken in a heavy duty type LPG lean-burn SI engine, to investigate the combustion process as it pertains to the pollutant formation process in the post flame region. Full spectra and band spectrum flame images were observed with a bottom view single cylinder research engine and two high speed cameras. NOx emissions were also measured for excess air ratios ranging from 1.0 to 1.6. A thermodynamic model, including the detailed chemical kinetic mechanism for LPG and NOx formation reactions, was developed to predict the major reaction species in the post flame region, and NOx emissions during the combustion process. The model qualitatively described the flame images for each band spectrum and could predict the measured NOx emissions very well.

Performance and emissions of an LPG lean burn engine for heavy duty vehicles were measured. The piston cavity, swirl ratio, propane - butane fuel ratio, and EGR were varied to investigate their effects on combustion, and thus engine performance. Three piston cavities were tested: a circular flat-bottomed cavity with sloped walls (called the “bathtub” cavity), a round bottomed cavity (called the “dog dish” cavity), and a special high-turbulence cavity (called the “nebula” cavity). Compared to the bathtub and dog dish cavities, the nebula type cavity showed the best performance in terms of cyclic variation and combustion duration. It was capable of maintaining leaner combustion, thus resulting in the lowest NOx emissions. High swirl improved combustion by achieving a high thermal efficiency and low NOx emissions. In general, as the propane composition increased, cyclic variation fell, NOx emissions increased, and thermal efficiency was improved.

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.

In this study, a piezo disk was used to generate a cloud of n-decane fuel drops, which were mixed with air, then carried into a combustion chamber and ignited by a platinum wire. Microgravity data obtained at the Japan Microgravity Center (JAMIC) were compared to normal gravity data, all at 1Atm pressure and 20+/-1°C initial temperature. Under normal gravity the lean limit was found to be 7.6x106/mm3 (Φ = 1.0), and from this point the flame front speed steadily increased from 20cm/s up to a maximum flame front speed of 210cm/s at a fuel drop density of about 14x106/mm3 (Φ = 1.85). Microgravity data showed a much richer lean limit - about 14.5x106/mm3 (Φ = 1.9), and the flame front speed did not gradually rise to a peak value. Instead, the measurements indicated a peak value of about 250cm/s, with a steep increase followed by a gradual decrease at richer fuel air ratios. A cellular flame structure appeared, and the cell size decreased as the mixture density increased.

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.

This paper deals with the process regarding how dehydrogenation of soot particles takes place. The measured carbon/hydrogen ratios plotted against mean-diameter of soots fall on a straight line passing through the origin. It is shown that in the course of soot particle growth CM ratio increases linearly with the particle diameter: D. This is an indication of the fact that the number of carbon grows in proportion to D3, whereas that of hydrogen is proportional to D2. It is there by concluded that hydrogen sit only on surface of soot particles.

The authors tried to use LP gas, mainly butane, as the main fuel of diesel engines to reduce soot and to maintain high thermal efficiency. LP gas was injected in the direction of the intake valve directly as a spray to prevent knocking and to preserve high charging efficiency. The newly developed electronic fuel injection provided accurate fuel control and injection timing. As a result, the dual-fuel operation produced high thermal efficiency almost identical to that of diesel engines. Soot in engine exhaust was almost negligible. Three quarters of maximum output was obtained with butane, and only small amount of gas oil for idling, in spite of an high compression ratio of 17 for gas engines. Increasing the proportion of gas oil resulted in maximum output from a diesel engine and almost no soot output.

This paper presents the result of a theoretical study on the effects of particle size distribution on the soot particle measurement method. The principal equations are rear-ranged into a concise form, and a wide variation of size distribution functions are introduced to calculate the effects. It was found that the mean extinction coefficient is very weakly dependent on the shape of size distribution functions and can be approximated to that for the Sauter mean diameter with insignificant error. The volumetric density of soot particles can be obtained by light transmittance measurement on a single wavelength, and this is affected only by the estimated value for the Sauter mean diameter. The error due to the estimation is under 5%. On the other hand, it was found that the light transmittance measurement is insufficient to obtain size distribution or the Sauter mean diameter of soot particles.

Remarkable progress has been made in recent years on pressure measuring techniques and apparatuses, yet they seem not necessarily successful in achieving accurate pressure diagrams at the high frequency range. The primary cause of difficulty lies in the occurrence of undesirable vibrations in the connecting passages which diminishes the accuracy of pressure diagrams. In order to prevent such vibration, the authors have attempted to increase the natural frequency in the connecting passages by enclosing heat resisting silicon oil, to analyse the frequency characteristics of the passages, and to ensure the propriety of the analysis through comparison with experiments. As a result, it is proved that the natural frequency of the silicon oil enclosed passage increases twice as high as that of the passage filled with working gas.

The authors designed and produced a new dual fuel injector that allows two different kinds of fuel to be injected. This injector contains both a throttle type nozzle and a hole type which are located coaxially. The injection timing as well as the fuel quantity can be controlled individually. The running test using two lines of gas oil brought a good reduction of NOx and exhaust smoke. The experiment using gas oil and alcohol also brought a satisfactory reduction of exhaust emission.