Search Results

A new method to simultaneously measure temperature and concentration distributions in unsteady gas jets was established with an adaptation of the laser-induced fluorescence of iodine molecules seeded into ambient gas. Using the temperature dependence of iodine fluorescence spectra, the local temperature inside jets was determined with the ratio between the fluorescence intensities of two visualized images with different wavelengths. Jet concentrations were also determined with the images for the temperature measurements. The method was applied to an unsteady argon jet injected into hot argon-iodine ambient gases. The experimental results showed that the local temperature distribution in an unsteady gas jet were quite similar to the local concentration distributions.

Diesel combustion and exhaust gas emissions under transient operation (when fuel amounts abruptly increased) were investigated under a wide range of operating conditions with a newly developed gas sampling system. The relation between gas emissions and piston wall temperatures was also investigated. The results indicated that after the start of acceleration NOx, THC and smoke showed transient behaviors before reaching the steady state condition. Of the three gases, THC was most affected by piston wall temperature; its concentration decreased as the wall temperature increased throughout the acceleration except immediately after the start of acceleration. The number of cycles, at which gas concentrations reach the steady-state value after the start of acceleration, were about 1.2 times the cycle constant of the piston wall temperature for THC, and 2.3 times for smoke.

Time-resolved and local ambient gas entrainment processes in intermittent gas jets with a range of injection conditions were evaluated by a LIFA (Laser-Induced Fluorescence of Ambient gas) technique. The gas injection conditions tested were: mean discharge velocity, um; mean discharge turbulence intensity, u′m; kinematic viscosity of the gas jet, ν; specific gravity of the gas jet, ρj; and of the ambient gas, ρa. Experimental results showed that the entrainment of jets are enhanced with higher eddy kinematic viscosity, νt, measured by a hot wire anemometer. In conclusion, the mean jet concentration was approximated with only one parameter, (ρj/ρa)D2/[(ν+νt)Δt].

Mixture formation processes of intermittent gas jets were visualized and quantified with high accuracy by a uniquely developed LIF technique (LIFA). Mixture strength inside gas jets was quantified by the fluorescence of iodine in the ambient gas excited by the sheet light of a Nd:YAG laser Two dimensional images of intermittent gas jets of various velocities were continuously recorded with VTR and quantified with high accuracy. The optimum conditions for measurements and accuracy with the LIFA technique were investigated. At the optimum setting of the initial iodine concentration in the ambient gas, accuracies better than 95% were obtained for the ambient gas entrainment ratio or jet concentration. The experimental results show that considerable amounts of ambient gas entrain just under the umbrella-like profile at the top of the jet. The mean jet concentration decreased with decreased nozzle diameter (D), and time elapsed after injection (Δt).

Diesel soot suppression effects of catalytic fuel additives for a range of fuels with different properties were investigated with calcium naphthenate. A single cylinder DI diesel engine and a thermobalance were used to determine the soot reduction and its mechanism for seven kinds of fuels. Experimental results showed that the catalytic effect of the fuel additive was different for the different fuels, and could be described by a parameter considering cetane number and kinematic viscosity. The fuel additives reduced soot more effectively for fuels with higher cetane number and lower kinematic viscosity. This result was explained by soot oxidation characteristics for the different fuels. Oxidation of soot with the metallic additive proceeds in two stages: stage I, a very rapid oxidation stage; and stage II, a following slow or ordinary oxidation stage.

The oxidations of Crapped diesel soots containing catalytic metals such as Ca, Ba, Fe, or Ni were characterized through thermogravimetric analysis with a thermobalance. Soot particles were generated by a single cylinder IDI diesel engine with metallic fuel additives. A two-stage oxidation process was observed with the metalcontalning soots. It was found that the first stage of oxidation is catalytically promoted by metal additives resulting in an enhanced reaction rate and a reduced activation energy. Soot reduction in the rapid first stage increases with increases in metal content. Soots containing Ba and Ca are oxidized most rapidly due to the larger reduction during the first stage. The second stage of oxidation is also slightly promoted by metal addition. The ignition temperature of the collected soot is substantially reduced by the metal additives.

Spark-assisted diesel engines operated with alcohol fuels usually display misfiring or knocking problems. This paper presents an analysis of the factors influencing the ignition characteristics of ethanol in a swirl chamber diesel engine with a multi-spark ignitor. In the experiments, cycle-to-cycle combustion variations and the degree of knocking were investigated by changing engine parameters over a wide operating range. The results of the investigations showed that stable ignition and smooth combustion is achieved when a flammable mixture is formed in the vicinity of the spark plug when only a small amount of the injected fuel has evaporated. By optimizing the design factors, operation with high efficiency and low exhaust emissions was achieved.

Forced ignition with glow plugs has great potential for the utilization of alcohol fuels in diesel engines. However, the installation of glow plugs may cause misfiring or knocking in parts of the operating range. This paper presents an analysis of the factors influencing the ignition characteristics of ethanol in a glow plug-assisted diesel engine; these factors may be classified into two categories: the factors related to the temperature history of the drop lets before contact with the glow plug, and those related to the probability of contact. By optimizing these factors, the combustion difficulties were successfully eliminated over the whole operating range, and engine performance comparable with conventional diesel operation was achieved.