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In order to investigate the soot formation process in a diesel spray flame, simultaneous imaging of soot precursor and soot particles in a transient spray flame achieved in a rapid compression machine was conducted by laser-induced fluorescence (LIF) and by laser-induced incandescence (LII) techniques. The 3rd harmonic (355nm) and the fundamental (1064nm) laser pulses from an Nd:YAG laser, between which a delay of 44ns was imposed by 13.3m of optical path difference, were used to excite LIF from soot precursor and LII from soot particles in the spray flame. The LIF and the LII were separately imaged by two image-intensified CCD cameras with identical detection wavelength of 400nm and bandwidth of 80nm. The LIF from soot precursor was mainly located in the central region of the spray flame between 40 and 55mm (270 to 370 times nozzle orifice diameter d0) from the nozzle orifice. The LII from soot particles was observed to surround the soot precursor LIF region and to extend downstream.

The two-dimensional distribution of a soot cloud in an unsteady spray flame in a rapid compression machine(RCM) was visualized using the laser sheet scattering technique. A 40 mm x 50 mm cross section on the flame axis was illuminated by a thin laser sheet from a single pulsed Nd:YAG laser(wavelength 532 nm). Scattered light from soot particles was taken by a CCD camera via a high speed gated image intensifier. The temporal variation of the scattered light images were presented with the injection pressure as a parameter. The results showed that scattered light was intense near the periphery of the flame tip and that the scattered light becomes weaker significantly and disappears fast after the end of injection as injection pressure is increased. This technique was also applied to the visualization of the two-dimensional distribution of liquid droplets in the non-evaporating spray to correlate it with the soot concentration distribution.

The concentrations of soot, NO and the other combustion products were measured by incylinder gas sampling in a DI diesel engine. The effects of injection timing, swirl ratio, and combustion chamber geometry on the formation and emission processes of soot and NO were studied. The following results were obtained: (1) Soot is promptly formed in the flame during the early combustion period where the equivalence ratio in the flame is high over 1.0. Thereafter almost all the formed soot is swiftly burnd up by oxidation during the middle combustion period. This process mainly determines the exhaust soot concentration. (2) NO is formed in the flame during the early and middle combustion period where the flame temperature is high over 2000 K. The highest NO concentration is observed at the flame tip swept by the air swirl. Though the concentration of the formed NO decreases by dilusion it nearly constant during the later combustion period.

A quasi-dimensional multi-zone model for diesel spray combustion has been developed. The model contains most of the physical processes of diesel spray combustion, and is simplified and economical. The zone formation is based on the fuel injection parameters. For the wall jet penetration velocity, a new equation is used based on the effect of the impinging free jet on the wall jet. For the fuel evaporation, an approximate solution of the instantaneous variations of droplet diameter is given in the simple algebraic equations based on the individual effect of the evaporation and the heat transfer from ambient gas. The soot emission sub-model calculates the soot concentration. This model has been applied for a direct injection diesel engine. The calculated results have shown a reasonable agreement with the experimental results. A parametric study has been carried out.

A new technique is developed for the in-situ measurement of Sauter mean diameter of droplets in non-evaporating transient dense sprays. This method analyzes the image of a shadowpicture of a spray based on the incident light extinction principle, and allows the sizing of Sauter mean diameter of whole droplets in a transient spray with any shape. In addition, this method allows the measurement of the local droplet size in a quasi-steady region of an axisymmetric spray if the conservation equations regarding mass and momentum are included in the calculation and data analysis. A calibration was carried out using glass beads as test particles: this was proved to have an accuracy of Sauter mean diameter measurement within 10%, on average. Applications of the new technique to both diesel and gasoline (EFI) sprays have been made.

The purpose of this study is to investigate the turbulent mixing in a diesel spray by large eddy simulation (LES). As the first step for the numerical simulation of diesel spray by LES, the LES of transient circular gas jets and particle laden jets were conducted. The simulation of transient circular jets in cylindrical coordinates has numerical instability near the central axis. To reduce the instability of calculation, azimuthal velocity around the central axis is calculated by the linear interpolation and filter width around the axis is modified to the radial or axial grid scale level. A transient circular gas jet was calculated by the modified code and the computational results were compared with experimental results with a Reynolds number of about 13000. The computational results of mean velocity and turbulent intensity agreed with experimental results for z/D>10. Predicted tip penetration of the jet also agreed to experimental data.

Development of the diesel particulate filter (DPF) aims to attain fast oxidation of accumulated soot at low temperature. Numerous researchers have explored the characteristics of soot oxidation under ambient conditions of simulated exhaust gas using thermogravimetric analysis or a flow reactor. In this study, temperature programmed oxidation (TPO) experiments were carried out for soot entrapped in miniaturized DPFs, cut-out from practical particulate filters, yielding wall-flow features typically encountered in real-world DPFs. Furthermore, when using the miniaturized samples, highly accurate lab-scale measurements and investigations can be facilitated. Examining different temperature ramping rates used for the TPO experiments, we propose a rate of 10°C/min as the most effective in analyzing soot oxidation in the practical filter substrates.

This paper presents a study of LPG lean burn in a motorcycle SI engine. The lean burn limits are compared by several ways. The relations of lean burn limit with the parameters, such as engine speed, compression ratio and advanced spark ignition etc. are tested. The experimental results show that larger throttle opening, lower engine speed, earlier spark ignition timing, larger electrode gap and higher compression ratio will extend the lean burn limit of LPG. The emission of a LPG engine, especially on NOx emission, can be significantly reduced by means of the lean burn technology.

The structure of dense sprays was investigated using 2-D imaging techniques. To investigate the mechanism of atomization, the liquid phase in a non-evaporating spray was visualized by a thin laser sheet formed by a single pulse from a Nd:YAG laser at the distance from 4 to 19 mm from the nozzle orifice with the injection pressure and the surrounding gas density as parameters. A new technique for the visualization of vapor phase in an evaporating spray, the SSI (Silicone particle Scattering Imaging) method, was proposed to investigate the structure of the vapor phase regions of the spray.

Internal combustion engines, as the dominant power source in the transportation sector and the primary contributor to carbon emissions, face both significant challenges and opportunities in the context of achieving carbon neutral goal. Biofuels, such as biodiesel produced from biomass, and zero-carbon fuel ammonia, can serve as alternative fuels for achieving cleaner combustion in internal combustion engines. The dual-fuel combustion of ammonia-biodiesel not only effectively reduces carbon emissions but also exhibits promising combustion performance, offering a favorable avenue for future applications. However, challenges arise in the form of unburned ammonia (NH3) and N2O emissions. This study, based on a ammonia-biodiesel duel-fuel engine modified from a heavy-duty diesel engine, delves into the impact of adjustments in the two-stage injection strategy on the combustion and emission characteristics.

In this study, the combustion characteristics of diesel flame achieved in a rapid compression and expansion machine (RCEM) at various patterns of oxygen distribution in the chamber are investigated in order to clarify the effect of heterogeneity of oxygen distribution in diesel engines induced by EGR on the soot and NOx emissions. To make the heterogeneous distribution of oxygen in a combustion chamber, the mixtures with different oxygen concentrations are injected through the each different port located on the cylinder wall. Results indicate that the amount of oxygen entrained into the spray upstream the luminous flame region affects the NO emission from diesel flame strongly.

Two kinds of planar soot imaging techniques, laser induced incandescence (LII) and laser induced scattering (LIS) techniques were applied simultaneously to an unsteady free spray flame achieved in a rapid compression machine. An analysis of LII and LIS images yielded three kinds of qualitative images of soot concentration, size of soot particles, and number density of soot in the flame. These images revealed the fact that the soot is formed mainly in the center region of a flame resulting in an appearance of soot cloud with high number density and small particle size in this region, and then the soot size increases and the number density decreases while soot is conveyed downstream.

The formation and oxidation processes of soot particles in unsteady spray flames were investigated in a quiescent atmosphere using 2-D laser sheet visualization. The mid-plane of a flame was illuminated twice during a short time-interval by a laser sheet from a double-pulsed YAG laser. An image pair of the scattered light from soot particles was taken by two intensified gated cameras in succession. The velocity vectors of soot clouds at various location in the sooting region were estimated using the spatial correlation between the image pair. The results of temporal and spatial variation of velocity and scattering intensity in the evolving soot clusters made it clear that soot is mainly formed in the periphery of the flame tip where the air entrainment is less and flame temperature favors soot formation.

A multi-functional membrane filter was developed through deposition of agglomerated Three-Way Catalyst particles with a size of 1 ~ 2 microns on the conventional bare particulate filter. The filtration efficiency reaches almost 100 % from the beginning of soot trapping with a low pressure drop and both reductions of NO and CO emission were achieved.

Acetone-Butanol-Ethanol (ABE), an intermediate product in the ABE fermentation process for producing bio-butanol, is considered a promising alternative fuel because it not only preserves the advantages of oxygenated fuel which typically emit less pollutants compared to conventional diesel, but also lowers the cost of fuel recovery for each individual component during the fermentation. With the development of advanced ABE fermentation technology, the volumetric percentage of acetone, butanol and ethanol in the bio-solvents can be precisely controlled. In this respect, it is desirable to estimate the performance of different ABE blends to determine the best blend and optimize the production process accordingly. ABE fuels with different component ratio, (A: B: E: 6:3:1; 3:6:1; 0:10:0, vol. %), were blended with diesel and tested in a constant volume chamber.

Stoichiometric dual-fuel compression ignition (SDCI) combustion has superior potential in both emission control and thermal efficiency. Split injection of diesel reportedly shows superiority in optimizing combustion phase control and increasing flexibility in fuel selection. This study focuses on split injection strategies in SDCI mode. The effects of main injection timing and pilot-to-total ratio are examined. Combustion phasing is found to be retarded in split injection when overmixing occurs as a result of early main injection timing. Furthermore, an optimised split injection timing can avoid extremely high pressure rise rate without great loss in indicated thermal efficiency while maintaining soot emission at an acceptable level. A higher pilot-to-total ratio always results in lower soot emission, higher combustion efficiency, and relatively superior ITE, but improvements are not significant with increased pilot-to-total ratio up to approximately 0.65.

Polyoxymethylene dimethyl ethers (PODEn) have high cetane number, high oxygen content and high volatility, therefore can be added to gasoline to optimize the performance and soot emission of Gasoline Compression Ignition (GCI) combustion. High speed imaging was used to investigate the spray and combustion process of gasoline/PODEn blends (PODEn volume fraction 0%-30%) under various ambient conditions and injection strategies in a constant volume vessel. Results showed that with an increase of PODEn proportion from 10% to 30%, liquid-phase penetration of the spray increased slightly, ignition delay decreased from 3.8 ms to 2.0 ms and flame lift off length decreased 29.4%, causing a significant increase of the flame luminance. For blends with 20% PODEn, when ambient temperature decreased from 893 K to 823 K, the ignition delay increased 1.3 ms and the flame luminance got lower.

Advanced compression ignition combustion system which reduces simultaneously both nitride oxides (NOx) and particulate matter (PM) is a promising approach to meet future emission regulations. In order to achieve advanced compression ignition, flexible fuel injection is required for ultra-early and post-TDC injections, which conventional injector fails to accomplish due to wall-wetting effect. In this work, special injectors with the spray angle of 60 degree are applied on a 4 cylinder mass-production diesel engine without modification of the engine configuration. For application-oriented study, sweep experiments of injection timings and durations, fuel injection pressure and the boost pressure are carried out to investigate the relationships between the control parameters and the engine performance. Model based calibration and real application tests validate the maximum applicable operation range of maximum speed of 2200 RPM and IMEP of 8.0 bar.

This paper presents experimental studies of particulate emissions in a small SI engine fueled with LPG and gasoline fuels. A single cylinder, four-stroke, water-cooled, 125cc EFI engine with gasoline fuel is used as the baseline engine. Characteristics of the particulate emissions of the two fuels are compared. Test results show that: there are great quantities of particulate emissions for both fuels, but the total numbers of particulate emissions for the two fuels are generally in the same level. The distribution of the particulate sizes is in bimodal type for the gasoline, but for the LPG its first peak is not markedly in some conditions. The particulate sizes of the second peak for the two fuels appear at about the same size. At middle loads and 3000r/min, the particulate emissions for both of the two fuels are the greatest.

A diesel particulate membrane filter (DPMF) offers good trapping efficiency of soot and reduces the pressure loss through the soot-trapping process. We found that one specific design of DPMF has the effect of reducing the apparent activation energy of the soot oxidation. The membrane is made of SiC nanoparticles with a diameter of 10-100 nm, which are covered with a thin silicon-oxy-carbide layer with a thickness of about 5 nm. The apparent activation energy of soot oxidation on the DPMF was reduced by 30-40 kJ/mol than conventional SiC-DPF. Furthermore, the light-off temperature of soot oxidation on the DPMF (with single nanosized Pt) is about 100°C lower than that of the DPMF (without Pt). The single nanosized Pt particles are embedded in the silicon-oxy-carbide layer. The formation of additional Pt is different from that which takes place in a conventional catalyzed soot filter (CSF). In a conventional CSF, the surface of the Pt particles is exposed to the atmosphere.