Yoshiteru Enomoto

AN EXPERIMENTAL ANALYSIS OF LOW-TEMPERATURE AND PREMIXED COMBUSTION FOR SIMULTANEOUS REDUCTION OF NOX AND PARTICULATE EMISSIONS IN DIRECT INJECTION DIESEL ENGINES

Abstract A new combustion concept, named MK (modulated kinetics) combustion, has been developed, which reduces NOx and smoke simultaneously through high exhaust gas recirculation (EGR) and retarded injection timing. High-speed photography was employed to investigate the physical and chemical processes of MK combustion, and the results revealed that the combustion features premixed combustion and the low-temperature flames were accompanied by transparent appearances. Heat flux measurements and KIVA calculations were also made to investigate the effects of swirl, which serves to improve thermal efficiency in MK combustion. It was apparent that the swirl effectively governs the fuel distribution in the combustion chamber, suppressing HC formation and improving thermal efficiency by preventing the flames from contacting the cavity walls. Throughout these experiments, ignition delay and fuel injection duration were found to be the two key parameters that control MK combustion. Accordingly, ignition delay was prolonged by cooled EGR and fuel injection duration was shortened by high injection pressure to allow the MK combustion operation in a high load range.

Heat loss to the combustion chamber wall with deposit in D.I. diesel engine: variation of instantaneous heat flux on piston surface with deposit

Abstract Adhesion of deposit on the combustion chamber walls affects the state of the heat loss into combustion chamber wall surfaces in the internal combustion engine. In this study, as the first step, the instantaneous surface temperature and the instantaneous heat flux were measured by thin film thermocouples on piston surfaces in the D.I. diesel engine with the adhesion of deposit in order to clarify the effects of deposit. As a result, it is found that the instantaneous surface temperature and heat flux strongly depend on the amount of deposit adhered to the combustion chamber wall surfaces.

Direct heat loss to combustion chamber walls in a direct-injection diesel engine: Evaluation of direct heat loss to piston and cylinder head

Abstract The purpose of this study is to clarify the state of the heat loss in a direct-injection diesel engine. Originally developed thin-film thermocouples (TFTs) are embedded into the combustion chamber walls for accurate measurement of instantaneous surface temperature from which instantaneous heat flux is evaluated through the heat conduction equation. Measured points are arrayed on the cavity bottom, the cavity side wall, the piston top, and the cylinder head. The TFTs are designed and fabricated so that disturbance of the temperature field is minimized when they are embedded into the combustion chamber walls. As a result, it is observed that the behaviour of instantaneous temperature and heat flux depends on the radius of the measured point. Measured points located radially inwards seem to be influenced by the combustion flame considerably more than those located outwards because the flame is presumed to stay in and around the cavity which occupies a region around the central axis of the piston. On the other hand, the heat loss ratio, namely the ratio of lost heat to the heat supplied by the fuel, is larger than in a gasoline engine.

Acceleration of Unsteady Incompressible Flow Calculation Using Extrapolation Methods

Acceleration techniques are important in computational fluid dynamics as scientists and engineers hope to shorten the computational time. Although the multigrid method has been successful in achievement of quick convergence, this approach tends to show poor performance in parallel computing with the domain decomposition technique, especially when a small number of grid points are assigned to one processor. Another shortcoming of the multigrid method is complicated numerical procedures.

Heat transfer coefficient on the combustion chamber wall surfaces in a naturally aspirated direct-injection diesel engine

Thin-film thermocouples were used to measure the instantaneous temperature at 100 points on all the combustion chamber wall surfaces in a naturally aspirated direct-injection diesel engine. Instantaneous heat flux at each measured point was also obtained through heat transfer analysis with the measured instantaneous wall surface temperature applied as a boundary condition. In addition, the instantaneous mass-averaged gas temperature in the combustion chamber was calculated through the equation of state of an ideal gas. As a result, the local and overall heat transfer coefficients were evaluated using the corresponding wall surface temperatures and heat fluxes. The overall heat transfer coefficients thus obtained were compared with those calculated with Eichelberg’s and Woschni’s empirical equations for five ignition timings and three engine speeds. As a result, it was revealed that an overall average heat transfer coefficient obtained through the authors’ experiments has characteristics different from those of the heat transfer coefficients calculated from the empirical equations proposed by Eichelberg and Woschni.

Parallel Computing of Flow in Centrifugal Fan Volute Using Contravariant Physical Velocity

Publisher Summary This chapter deals with parallel computing of flow in centrifugal fan volute using contravariant physical velocity. In terms of engineering applications of computational fluid dynamics (CFD), high accuracy and affordable computational costs are required and PC clusters are regarded as promising tools. Boundary fitted coordinates (BFCs) are usually introduced to CFD codes to represent complicated configurations in engineering applications unless an unstructured grid is employed. For incompressible flow of complex geometry, variables such as Cartesian velocity components and pressure are usually collocated on a grid. In addition, Rhie–Chows method is often included in the solver to avoid the pressure oscillation. This chapter discusses implementation of a Navier–Stokes solver using contravariant physical velocity on a PC cluster to predict flow in a centrifugal fan volute. Parallelization is based on the domain decomposition technique with message passing provided by the MPI. Up to eight processors are used. Predicted flow patterns and volute performance agree well with experimental results. In spite of uneven load distribution and complicated communication patterns required in the near-tongue treatment, efficiency per iteration is 0.767 with four processors and 0.760 with eight.

Development of thin-film thermocouple measuring for instantaneous heat flux flowing into the ceramic combustion chamber wall

In order to evaluate the validity of a low heat rejection engine proposed for the reduction of heat loss, a thin film thermocouple was developed for accurate measurement of the instantaneous heat flux flowing into the ceramic combustion chamber wall. The thin film thermocouple is the pair-wire type construction without effects of the material of the thermocouple and the instantaneous heat flux, which was confirmed by finite element analysis. This paper also shows examples of measurements conducted on the instantaneous heat flux flowing into the ceramic combustion chamber, using the pairwire type thin film thermocouple made of ceramic base material.