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Technical Paper

Direct Heat Loss to Combustion Chamber Walls in a D.I. Diesel Engine-Development of Measurement Technique and Evaluation of Direct Heat Loss to Cylinder Liner Wall

The purpose of this study is to clarify the state of heat loss to the cylinder liner of the tested engine of which piston and cylinder head were previously measured. The authors' group developed an original measurement technique of instantaneous surface temperature at the cylinder liner wall using thin-film thermocouples. The temperature was measured at 36 points in total. The instantaneous heat flux was calculated by heat transfer analysis using measurement results of the temperature at the wall. As a result, the heat loss ratio to all combustion chamber walls is evaluated except the intake and exhaust valves.
Technical Paper

The Effect of Knock on Heat Loss in Homogeneous Charge Compression Ignition Engines

One of the problems in HCCI combustion is a knocking in higher load conditions. It governs the high load limit, and it is suggested that the knock increases heat loss[1], because it breaks the thermal boundary layer. But it is not clear how much knock affects on heat loss in the HCCI combustion in various conditions, such as ignition timing and load. The motivation of this study is to clarify the ratio of heat loss caused by knock in HCCI engines. The heat loss from zero-dimensional calculations with modified heat transfer coefficient, which is considering the effect of knock by adding a term of cylinder pressure rising rate dp/dt, agreed well with the results from the thermodynamic analysis in various conditions. And the results show that it is possible to avoid heat loss by knock by controlling the ignition timing at appropriate timing after T.D.C. and it will be possible to expand the load range if knock can be avoided.
Technical Paper

Measurement of Instantaneous Heat Flux Flowing Into Metallic and Ceramic Combustion Chamber Walls

Accurate measurements of combustion gas temperature and the coefficient of heat transfer between the gas and the combustion chamber wall of internal combustion engine in cyclic operations are difficult at present. Hence the only method available for determination of states of thermal load and heat loss to the combustion chamber wall in a cycle is to measure the instantaneous temperature on the combustion chamber wall surface accurately and precisely using proper thin-film thermocouples, then to calculate the instantanenous heat flux flowing into the wall surface by means of numerical analysis. However, it is necessary to pay adequate attention to the effects of thermophysical properties of the thermocouple materials on the measured values, since any thermocouple consists of several kinds of materials which are different from those of portions to be measured.
Technical Paper

A Study of Heat Rejection and Combustion Characteristics of a Low-temperature and Pre-mixed Combustion Concept Based on Measurement of Instantaneous Heat Flux in a Direct-Injection Diesel Engine

There have been strong demands recently for reductions in the fuel consumption and exhaust emissions of diesel engines from the standpoints of conserving energy and curbing global warming. A great deal of research is being done on new emission control technologies using direct-injection (DI) diesel engines that provide high thermal efficiency. This work includes dramatic improvements in the combustion process. The authors have developed a new combustion concept called Modulated Kinetics (MK), which reduces smoke and NOx levels simultaneously by reconciling low-temperature combustion with pre-mixed combustion [1, 2]. At present, research is under way on the second generation of MK combustion with the aim of improving emission performance further and achieving higher thermal efficiency [3]. Reducing heat rejection in the combustion chamber is effective in improving the thermal efficiency of DI diesel engines as well as that of MK combustion.
Technical Paper

Heat Transfer into Ceramic Combustion Chamber Wall of Internal Combustion Engines

The authors developed the optimum thin film thermocouples in terms of materials, shape and dimensions to make instantaneous surface temperature and heat flux measurements of combustion chamber wall in internal combustion engines with accuracy by the computer analysis. And they succeeded to make thin film thermocouple in ceramic piston, by the application of the above technique. Then, the instantaneous surface temperature was measured to obtained the instantaneous heat flux on the ceramic plate fixed on top of the piston.
Technical Paper

Heat Transfer into Ceramic Combustion Wall of Internal Combustion Engines

A thin film thermocouple with a high accuracy was developed by means of computer analysis, which allowed measurements of instantaneous temperatures and heat fluxes on combustion chamber walls. Conventional Al-alloy and ceramic plates were compared in terms of the heat loss at the upper surface of each piston during combustion, using a gasoline engine and a diesel engine in the series of experiments. It was found by the comparison that the ceramic plates subjected to higher temperatures had greater heat losses in both the gasoline and diesel engines contrary to the anticipation.
Technical Paper

Effects of Flame Motion and Temperature on Local Wall Heat Transfer in a Rapid Compression-Expansion Machine Simulating Diesel Combustion

Local heat flux from the flame to the combustion chamber wall, q̇, was measured the wall surfaces of a rapid compression-expansion machine which can simulate diesel combustion. Temperature of the flame zone, T1, was calculated by a thermodynamic two-zone model using measured values of cylinder pressure and flame volume. A local heat transfer coefficient was proposed which is defined as q̇/(T1-Tw). Experiments showed that the local heat transfer coefficient depends slightly on the temperature difference, T1-Tw, but depends significantly on the velocity of the flame which contacts the wall surface.