Search Results

Numerical calculations based on large eddy simulation were performed in order to investigate mixture formation, ignition, and combustion processes in a diesel spray formed by fuel injection into a constant-volume vessel under high-temperature and high-pressure conditions. Fuel concentration distributions in a spray and local non-homogeneous mixture distributions were compared with experimental results to verify the accuracy of the calculations. In addition, calculations were carried out to examine the effect of injection parameters, namely, injection pressure and nozzle orifice diameter. Ignition and combustion processes were also investigated using Schreiber's model for calculating the progress of oxidation reactions.

Formation of nitrogen oxides (NOx) in direct-injection premixed charge compression ignition (DI-PCCI) combustion simulated in a constant volume vessel was investigated using an ignition-combustion model that combines a stochastic mixing model with a reduced chemical reaction scheme. Several improvements were made to the model in order to predict the combustion processes in DI-PCCI. Calculations were carried out for the injection and ambient conditions equivalent to the measurements using the constant volume vessel. Analysis of the calculated results clarified the effects of mixture heterogeneity on NO concentrations and the mechanisms are discussed. The results show that the model successfully represents the experimental tendency for NO concentration when the injection conditions and ambient oxygen mole fraction are varied.

The objective of the present study is to elucidate the combustion process of partial premixed charge compression ignition (PCCI) combustion using multiple injections in diesel engines. The effects of the ratio of the quantity of fuel used in the first and second injections, and the injection dwell time on heat release rate, soot and nitrogen oxide (NOx) formations are investigated in simulated partial PCCI combustion using a constant-volume vessel. N-heptane is used as fuel. The experiments are carried out under an ambient condition of 2 MPa and 900 K, which simulates a PCCI-like heat release rate with long ignition delays. The oxygen concentration is set to 21 and 15% to simulate conditions without and with exhaust-gas recirculation (EGR), respectively. The fuel quantity in the first injection is varied between 10 to 40% of the total fuel quantity, and the injection dwell is varied between 0.5 to 2.0 ms.

In order to obtain fundamental data to employ direct injection in gas-fueled engines, an experimental study was carried out using a constant volume vessel. Heat release rates and shadowgraph photos were acquired for natural-gas and hydrogen jets simulating the changes in engine-combustion-control factors. The results show that although a higher temperature is needed for ignition, the temperature dependencies of ignition delay and heat release rate in natural-gas jets are similar to those of diesel sprays. The ignition delay and heat release rate are sensitive to injection and ambient conditions. Hydrogen jets have shorter ignition delays compared with natural gas jets. At sufficiently high ambient temperatures, the heat release pattern shows an entire diffusion combustion. Under such conditions, the ignition delay is not greatly influenced by injection conditions and the heat release rate can be controlled by the injection rate.

Numerical calculations were performed to investigate the mixture formation, ignition, and combustion processes in a diesel spray. The spray was formed by injecting n-heptane into a constant volume vessel under high-temperature and high-pressure conditions. The fuel droplets were described by a discrete droplet model (DDM). Numerical calculations for the flow and turbulent diffusion processes were performed on the basis of large eddy simulation (LES) to describe the processes of local non-homogeneous mixture formation and heat release. The oxidation processes in the mixture were calculated by Schreiber's five-step mechanism for n-heptane. Calculations were performed for sprays formed by single-stage injection and pilot/main two-stage injection. The flame structure in a diesel spray and its temporal change were discussed using a flame index proposed by Yamashita et al.

Single-excite dual-fluorescence PLIF was applied to a diesel spray of a two-component fuel, the components of which have different boiling points. The spray was formed by injecting fuel into a constant-volume vessel under high-temperature, high-pressure conditions. The fluorescence emitted from the two tracers for the fuel was optically separated to measure the concentration of each component. Mixture formation was investigated based on the concentration distributions of each fuel component. The fuel concentration was derived based on the change in fluorescence intensity due to temperature and the assumption of adiabatic mixing of fuel and the surrounding fluid. The variation in the mixture distribution due to differences in the vaporization characteristics was investigated, and the results revealed that the two components have similar distribution. The concentration of the high-boiling-point component increased upstream region in a spray.