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Ignition by Nanosecond Repetitively Pulsed Discharges (NRPD) at EXponential Increase of Minimum Ignition Energy (MIE-EXI) region under super lean SI engine conditions was studied. Fundamental experiments were conducted with a turbulent ignition test chamber with twin counter-rotating fans. The MIE-EXI region by arc discharge appeared over 6500 rpm of fan speed. In the MIE-EXI region (7000 rpm), successful ignition was achieved by establishing coupled ignition kernels with NRPD at 15 kHz although ignition was unsuccessful at 1 kHz. Results show that ignition by NRPD has potential advantages for lean burn applications. Preliminary engine test results with NRPD were also demonstrated.

The thermal efficiency of internal combustion engines can be improved dramatically with the right combination of engine technology and fuel technology. Super lean-burn technology is attracting attention as a means of boosting thermal efficiency. However, there is a limit to how lean a fuel-air mixture can be before combustion becomes unstable or misfire occurs. The authors evaluated the effects of various chemical compositions on the lean limit under super lean-burn conditions. By changing the composition of the fuel, it was possible to achieve excess air ratios of over 2.0, resulting in high thermal efficiency.

Lean burn is one method for improving thermal efficiency in spark ignition (SI) engines. Suppression of knocking provides higher thermal efficiency, and ethanol blending is considered an effective way to suppress knocking due to its high octane and high latent heat of evaporation. We investigate the effect of ethanol blending on knocking in an SI engine under lean operating conditions. The Livengood-Wu (LW) integral was performed based on ignition delay duration estimated from a zero-dimensional detailed chemical reaction calculation with pressure and temperature histories. Knocking was suppressed and thermal efficiency increased with ethanol-gasoline blending fuel, even at 0.5 equivalence ratio. Decrease in unburned gas temperature by latent heat of evaporation had a comparable influence on knocking suppression, which was supported by LW integral analysis.

To adhere to stringent environmental regulations, SI (spark ignition) engines are required to achieve higher thermal efficiency. In recent years, EGR (exhaust gas recirculation) systems and lean-burn operation has been recognized as key technologies. Under such operating conditions, reducing CCV (cycle-to-cycle variation) in combustion is critical to the enhancement of overall engine performance. Flow-field CCV is one of the considerable factors affecting combustion in engines. Conventionally, in research on flow fields in SI engines, the ensemble average is used to separate the measured velocity field into a mean component and a fluctuation component, the latter of which contains a CCV component and a turbulent component. To extract the CCV of the flow field, previous studies employed spatial filter, temporal filter, and POD (proper orthogonal decomposition) methods.

It has been shown that lean burn is effective for improving the thermal efficiency of gasoline SI engines. This happens because the reduction of heat loss by decrease of flame temperature. On the other hand, the fuel dilution of the premixed gas makes the combustion speed low, and cycle-to-cycle variations of combustion are increased by excessive dilution, it is difficult to increase the thermal efficiency of the gasoline SI engine. Influence of ignition by spark discharge is considered as a factor of combustion variation, and it is necessary to understand the effects of spark discharge characteristics on the lean combustion process. Spark discharge in the SI engines supplies energy to the premixed-gas via a discharge channel in the spark plug gap which ignites the premixed-gas. The discharge channel is elongated by in-cylinder gas flow and its behavior varies in each cycles.

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.

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.

The characteristics of cycle-to-cycle variations of indicated mean effective pressure (IMEP) with combustion-phasing retard have been investigated experimentally and computationally in an homogeneous charge compression ignition (HCCI) engine using dimethyl ether (DME). The experiments were conducted in a single-cylinder HCCI research engine equipped with an exhaust gas recirculation (EGR) passage for external EGR and a two-stage exhaust cam for rebreathed EGR. To understand the chemical effects of rebreathed EGR, which is assumed to contribute to the autoignition enhancement, the computations were performed with a single-zone model of CHEMKIN using a chemical-kinetic mechanism developed by combining DME mechanism and NOx submechanism.

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.

This study tried to find a potential of dedicated EGR (d-EGR) system added to the four-cylinder spark ignition (SI) engine to decrease heat loss (Qheatloss) and improve thermal efficiency (ηth). Test fuels were chosen by methane and propane. PREMIX code in CHEMKIN-PRO was employed to calculate laminar burning velocity (SL) and flame temperature (Tf). Wiebe function and Wocshni's heat transfer coefficient were considered to calculate ηth. The results show that the d-EGR system increased ηth and it was higher than that of stoichiometric combustion of conventional SI engines due to the low Tf and fast SL.

The dynamics model and model-based controller (LQG servo controller) have been constructed to improve performance of diesel engine in transient condition. The input parameters of the model are fuel quantity of main injection, timing of main injection, fuel quantity of pilot injection, timing of pilot injection, external EGR ratio and boost pressure. The parameters that are succeeded between cycles to express transient condition are residual gas temperature and of residual oxygen. In the model, one cycle is discretized into 10 representative points. The precision of the accuracy of the model and the responsiveness of the controller were confirmed.

This study computationally investigates the combined effects of EGR and boost pressure on HCCI autoignition using iso-octane, PRF50 and n-heptane. The computations were conducted using the single-zone model of CHEMKIN included in CHEMKIN-PRO with detailed chemical-kinetics mechanisms for iso-octane, PRF and n-heptane from Lawrence Livermore National Laboratory (LLNL). To better reproduce the state of EGR addition in real engine, the EGR composition is determined after several combustion cycles under the constant amount of fuel. All data points were acquired with a CA50 of 5°CA aTDC by adjusting initial temperature to remove the effect of combustion phasing, which can influence on HCCI autoignition from any effect of the EGR and boost pressure themselves. The results show that EGR increases the burn duration and reduces the maximum pressure-rise rate with lower peak of maximum heat-release rates for all fuels even for a boost pressure, which accelerates a HCCI autoignition propensity.

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.

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.

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.

The HCCI combustion mode poses its own set of narrow engine operating by knocking. In order to solve this, inhomogeneity method of mixture and temperature is suggested. The purpose of this research is to get fundamental knowledge about the effect of thermal stratification on HCCI combustion of n-Heptane/iso-Octane-Air mixture. The temperature stratification is made by buoyancy effect in combustion chamber of RCM. The analysis items are pressure, temperature of in-cylinder gas and combustion duration. In addition, the structure of flames using the two dimensional chemiluminescence's images by a framing camera are analyzed. Under stratification, the LTR starting time and the HTR starting time are advanced than that of homogeneous. Further, the LTR period of homogeneous conditions became shorter than that of the stratified conditions. . With the case of homogeneous condition, the luminosity duration becomes shorter than the case of stratified condition.

Homogeneous Charge Compression Ignition (HCCI) engine attracts much attention because of its high thermal efficiency and low NOx, PM emissions. On the other hand, Di-Methyl Ether (DME) is expected as one of alternative fuel for the internal combustion engines. In this study, four-stroke HCCI engine running on DME is developed to make it realistic application in production engines. This paper shows construction of the control method using both internal EGR at high temperature and external EGR at low temperature and estimates the performance of developed HCCI engine. Besides combustion characteristics of DME and the effects of EGR are researched with experiment and numerical calculation with elementary reactions. As a result, developed HCCI engine got comparable high thermal efficiency to conventional diesel engine but much lower Indicated Mean Effective Pressure (IMEP) than that. Meanwhile it can be said that DME is suitable fuel for the HCCI engines in combustion characteristics.

In order to clarify the reason why NOx emissions factor becomes higher at vehicle acceleration at intersections etc, two freight vehicles, that have EGR system for the reduction of NOx, were tested by an on-board NOx measurement system. Higher NOx emissions factor was observed in operations in lower-gear operation for each vehicle. Since the engine speed change was higher in the operation of lower gears, NOx emissions characteristics were analyzed in view of engine torque, NOx mass emissions and EGR rate, considering engine speed change. It was found that lower-gear operations made the engine speed change higher and the EGR rate lower. This seems to be one of the factors to engender the intensive NOx pollution at roadsides.

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.

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.