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A significant drawback to HCCI engines is the knocking caused by rapid increases in pressure. Such knocking limits the capacity for high-load operation. To solve this problem, thermal stratification in the combustion chamber has been suggested as possible solution. Thermal stratification has the potential to reduce the maximum value of the rate of pressure increase combustion by affecting the local combustion start time and extending the duration of combustion. The purpose of this study was to experimentally obtain fundamental knowledge about the effect of thermal stratification on the HCCI combustion process. Experiments were conducted in a rapid compression machine (RCM) equipped with a quartz window to provide optical access to the combustion chamber. The machine was fueled with DME, n-Butane, n-Heptane and iso-Octane, all of which are currently being investigated as alternative fuels and have different low temperature characteristics.

Theoretically, homogeneous charge compression engines (HCCI) are able to grant a high thermal efficiency, as well as a low NOx and particulate emissions. This ability is mainly due to the combustion process, which, contrary to both Diesel and Gasoline engine, is homogeneous in time and space within the combustion chamber. But despite these advantages, the engine operating condition is limited by the narrow boundaries of misfire at low load and knocking at high load. For that matter, one of the numerous ways of overcoming knocking is to deliberately create fuel inhomogeneities within the combustion chamber, since it has proved to lengthen combustion duration and to drastically reduce maximum pressure rise rate (PRR). Nevertheless, though the global effects of fuel inhomogeneities on PRR have been studied, we lack information that explains this phenomenon.

In this study, the effects of fuel properties, aromatics content and 90% distillation temperature T90, on flame temperature and soot formation were studied using a rapid compression machine (RCM). Aromatics content and T90 distillation temperature were parameters isolated from influence of each other, and from cetane number. A fuel spray was injected in the RCM combustion chamber by a single nozzle hole. The ignition and combustion processes of diesel spray were observed by a high-speed direct photography. Flame temperature and KL factor (which indicates the soot concentration), were analyzed by the two-color method. The rate of heat release was analyzed from indicated diagrams. The fuels with aromatics content showed higher flame temperature. The fuel with highest T90 distillation temperature showed highest flame temperature.

In this study, effects of nozzle hole diameter and EGR ratio on flame temperature (indication of NO formation) and KL value (indication of soot formation) were investigated. Combustion of a single diesel fuel spray in the cylinder of a rapid compression machine (RCM) was analyzed. Three nozzles with different hole diameter were used corresponding to present, near term and long term heavy duty diesel engine specifications. EGR was simulated through 2%vol. CO2 addition to the inlet air and by increase of in-cylinder surrounding gas temperature. Various types of fuels were used in this. The ignition and combustion processes of diesel fuel spray were observed by a high-speed direct photography and by indicated pressure diagrams. Flame temperature and KL factor were analyzed by a two-color method. With larger nozzle hole diameters there are larger high temperature areas. With smaller nozzle hole diameters there is more soot formed. Introduction of 2% vol.

In the HCCI Engine, inhomogeneity in fuel distribution and temperature in the pre-mixture exists microscopically, and has the possibility of affecting the ignition and combustion process. In this study, the effect of charge inhomogeneity in fuel distribution on the HCCI combustion process was investigated. Two-dimensional images of the chemiluminescence were captured by using a framing camera with an optically accessible engine in order to understand the spatial distribution of the combustion. DME was used as a test fuel. By changing a device for mixing air and fuel in the intake manifold, inhomogeneity in fuel distribution in the pre-mixture was varied. The result shows that luminescence is observed in a very short time in a large part of the combustion chamber under the homogeneous condition, while luminescence appears locally with considerable time differences under the inhomogeneous condition.

This work has been investigated the potential of in-cylinder EGR stratification for reducing the pressure rise rate of DME HCCI engines, and the coupling of both thermal stratification and fuel stratification. The numerical analyses were done by using five-zone version of CHEMKIN-II kinetics rate code, and kinetic mechanics for DME. The effects of inert components were used for the presence of EGR in calculation. Three cases of EGR stratification were tested on both thermal stratification and fuel stratification at the fixed initial temperature, pressure and fueling rate at BDC. In order to explore the appropriate stratification of EGR, EGR width was employed from zero to thirty percent. Firstly, EGR homogeneity case which means EGR width zero was examined. Secondly, EGR is located densely in hotter zone for combining with thermal stratification or in richer zone for a combination with fuel stratification. Lastly, the case was judged inversely with the second case.

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.

The time of, and location where ignition first occurs in a diesel fuel spray were investigated in a rapid compression machine (RCM) using the two–dimensional techniques of silicone oil particle scattering imaging (SSI), and the planar laser induced fluorescence (LIF) of formaldehyde. Formaldehyde has been hypothesized to be one of the stable intermediate species marking the start of oxidation reactions in a transient spray under compression ignition conditions. In this study, the LIF images of the formaldehyde formed in a diesel fuel spray during ignition process have been successfully obtained for the first time by exciting formaldehyde with the 3rd harmonic of the Nd:YAG laser. SSI images of the vaporizing spray, and the LIF images of formaldehyde were obtained together with the corresponding time record of combustion chamber pressures at initial ambient temperatures ranging from 580 K to 790 K.

HCCI (Homogeneous Charge Compression Ignition) engine has a problem which causes knocking when the maximum PRR (Pressure Rise Rate) reaches a certain level because it takes the form of combustion of simultaneous multi-point ignition by compression of the air-fuel pre-mixture. This study focused on stratified charge of fuel in combustion chamber. This method disperses the timing of local ignition. The distribution of fuel concentration is measured by using LIF (Laser Induced Fluorescence). As a result, the maximum PRR is reduced by stratified charge of fuel. In addition, it is confirmed that the dispersion of combustion timing depends on the dispersion of fuel concentration.

In PCCI combustion with multiple injections, the mechanism having two heat release peaks which has a favorable characteristic of reducing noise is studied using numerical tool of single- and also multi-zone model of CHEMKIN PRO. In the present investigation, the physical issues, such as variations in the equivalent ratio and temperature caused by the fuel injection are simplified first so that the key issues of chemical reaction occurred in the combustion chamber can be extracted and are discussed in detail. The results show that the interval of two heat-release peaks can be controlled and as the number of zones of the calculation increases, the change in the timing of a heat release peak is increased but over three-zones, it is not affected any more. This indicates that to study about complex diesel combustion phenomena, three-to four-zone model shall give sufficiently accurate results.

Thermal and mixing stratifications have been thought as one of the ways to avoid an excessive pressure rise on HCCI combustion. The purpose of this research is to investigate the potential of thermal and mixing stratifications for reducing PRR (Pressure Rise Rate) on HCCI combustion. The pre-mixture with thermal and mixing stratifications is charged in RCM (Rapid Compression Machine). After that, the pre-mixture is compressed and in that process, in-cylinder gas pressure and chemiluminescence images are obtained and analyzed. Furthermore, experimental results are compared with the computational results calculated by using multi-zone model for analyzing these mechanisms.

Super lean burn technology is conceived as one of methods for improving the thermal efficiency of SI engines[1][2]. For lean burn, reduction of heat loss and the due to decrease in flame temperature can be expected. However, as the premixed gas dilutes, the combustion speed decreases, so the combustion fluctuation between cycles increases. Also, to improve the thermal efficiency, the ignition timing is advanced to advance the combustion phase. However, when the combustion phase is excessively advanced, knocking occurs, which hinders the improvement of thermal efficiency. Knocking is a phenomenon in which unburned gas in a combustion chamber compressed by a piston and combustion gas suffer compression auto-ignition. It is necessary to avoid knocking because the amplitude of the large pressure wave may cause noise and damage to the engine. Also, knocking is not a steady phenomenon but a phenomenon that fluctuates from cycle to cycle.