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To allow the HCCI vehicles to enter the market in the future, it is important to investigate the combustion deviations and operational range differences between the same research octane number fuels. In this paper, eighteen kinds of two hydrocarbon blended fuels, which were composed of n-heptane and another hydrocarbon, such as iso-octane, diisobutylene, 4-methyl-1-pentene, toluene or cyclopentane, were evaluated. Those fuels were blended to have the same research octane numbers of 75, 80, 85 and 90 by changing the blending volume ratio of n-heptane and counterpart hydrocarbon. Intake air was supercharged to 155 kPa abs and its temperature was kept at 58 °C. The HCCI engine was operated at 1000 rpm. Neither hot EGR, nor any other combustion stratification system was utilized in order to investigate the purely hydrocarbon effects on HCCI combustion.

It was reported that n-heptane and toluene blended fuels (NTL series fuels) showed the dual phase high temperature heat release (DP-HTHR) combustion in a previous SAE paper [1]. DP-HTHR has the potential to enlarge the engine operational range to high load conditions and lower the engine combustion noise. Further research has been reported in this paper. Initial interests were in the combustion characteristics of a second “bump” in the high temperature heat release (2nd HTHR) in DP-HTHR, since this kind of two-stage combustion appears, when CO oxidation radically occurs over the 1450K temperature range.

It is well known that ultra-lean combustion can result in higher thermal efficiency, better fuel economy, and greatly reduced NOx emissions. Accomplishing ultra-lean combustion is very difficult with a conventional spark plug, and ignition instability can be cited as one of the factors. Therefore, it is thought that ignition system innovation is important for the achievement of ultra-lean combustion in gasoline engines. This study investigated high-speed plasma ignition as a new ignition system for internal combustion engines. High-speed plasma refers to the transient (non-equilibrated) phase of plasma before formation of an arc discharge; it is obtained by applying high voltage with an ultra-short pulse between coaxial cylindrical electrodes. High-speed plasma can inherently form a multi-channel discharge, with the electrical discharge spreading over a much larger volume than a spark discharge does.

Control of turbulence during the compression stroke is suggested by both theoretical calculations and experimental results obtained with an LDV measurement in a motored engine. The authors have found experimentally that when an axial distribution of swirl intensity exists, a large-scale annular vortex is formed inside the cylinder during the compression stroke and this vortex generates and transports turbulence energy. A numerical calculation is adopted to elucidate this phenomenon. Then, an axial stratification of swirl intensity is found to generate a large-scale annular vortex during the compression stroke by an interaction between the piston motion and the axial pressure gradient. The initial swirl profile is parametrically varied to assess its effect on the turbulence parameters. Among calculated results, turbulence energy is enhanced strongest when the swirl intensity is highest at the piston top surface and lowest at the bottom surface of the cylinder head.

According to previous papers on the combustion process in LHR diesel engines the combustion seems to deteriorate in LHR diesel engines. However it has been unclear whether this was caused by the high temperature gas or high temperature combustion chamber walls. This study was intended to investigate the effect of gas temperature on the rate of heat release through the heat release analysis and other measurements using a rapid compression-expansion machine. Experiments conducted at high gas temperatures which was achieved by the employment of oxygen-argon-helium mixture made it clear that the combustion at a high gas temperature condition deteriorated actually and this was probably due to the poorer mixing rate because of the increase in gas viscosity at a high gas temperature condition.

This paper describes simultaneous attainment in improving fuel consumption, output power and reducing HC emissions with a direct injection S.I. engine newly developed in Nissan. Straight intake port is adopted to increase discharge coefficient under WOT operation and horizontal swirl flow is generated by a swirl control valve to provide stable stratified charge combustion under part load conditions. As a result, fuel consumption is reduced by more than 20% and power output is improved by approximately 10%. Moreover, unburned HC is reduced by equivalently 30% in engine cold start condition. An application of diagnostic and numerical simulation tools to investigate and optimize various factors are also introduced.

The applicability of several popular diesel particulate matter (PM) measurement techniques to low temperature combustion is examined. The instruments' performance in measuring low levels of PM from advanced diesel combustion is evaluated. Preliminary emissions optimization of a high-speed light-duty diesel engine was performed for two conventional and two advanced low temperature combustion engine cases. A low PM (<0.2 g/kg_fuel) and NOx (<0.07 g/kg_fuel) advanced low temperature combustion (LTC) condition with high levels of exhaust gas recirculation (EGR) and early injection timing was chosen as a baseline. The three other cases were selected by varying engine load, injection timing, injection pressure, and EGR mass fraction. All engine conditions were run with ultra-low sulfur diesel fuel. An extensive characterization of PM from these engine operating conditions is presented.

To investigate the ignition process in a diesel spray, the ignition in a transient fuel spray is analyzed numerically by a simple quasi-steady spray model coupled with the Shell kinetics model at various operating conditions and validity of this model is assessed by a comparison with existing experimental data. The calculated results indicate that the competition between the heat absorption of fuel and the hot air entrainment determines the equivalence ratio of mixtures favorable for the ignition to occur in the shortest time.

Computation of the three-dimensional flow in the intake ports and the cylinders of real engines, including moving valves and piston, has been carried out by solving the Navier-Stokes equations. No explicit turbulence models are used. An extended version of the SIMPLE and ICE method is employed to simulate density variations in engines, which are connected with compression rate, heat transfer, and compressibility. A third-order upwind scheme is combined with this method. Computational results show complex flow fields such as separated flows near the valve seat and small vortices of the order of the mesh size near the end of compression. These computational results are compared with the LDV measurements.

It is known that the regular gasoline and primary reference fuel (PRF), that have the same research octane number, show the different HCCI engine performance, because of the different phasing and heating value of low temperature heat release. This means that the research octane number is not an “all-round” auto-ignition index, and another index must be developed to evaluate the HCCI combustion characteristics. In this paper, eleven pure hydrocarbon components were blended into twenty three different kinds of model fuels (surrogate fuels), labeled BASE, MC01-MC11 and K01-K11, and the HCCI engine tests were performed under five different intake air temperature conditions to change the auto-ignition characteristic of each hydrocarbon component. As HCCI combustion can be described as a lean and slow gasoline knocking phenomenon, an analysis of HCCI combustion data gives us much more important knowledge of gasoline knocking phenomenon.

Since the stable operating region of a gasoline-fueled HCCI engine is limited to the part load condition, a mode change between SI and HCCI combustion is required, which poses an issue due to the difference in combustion characteristics. This report focuses on the combustion characteristics in the transitional range. The combustion mode in the transitional range is investigated by varying the internal EGR rate, intake air pressure, and spark advance timing in steady-state experiments. In this parametric study, stable SI-CI combustion is observed. This indicates that the combustion mode transition is possible without misfiring or knocking, regardless of the speed of variable valve mechanism which includes VVA, VVEL, VTEC, VVL and so on, though the response of intake air pressure still remains as a subject to be examined in the actual application.

An HCCI combustion has a low temperature heat release (LTHR) and a high temperature heat release (HTHR). During the LTHR period, fuel chemicals break down into radicals and small hydrocarbons, and they assist an initial reaction of HTHR. This is an important role of LTHR. On the contrary, LTHR has a negative aspect. In general, a heating value of LTHR changes depending on HCCI engine load due to the difference of the injected fuel quantity. The heating value of LTHR is low under low load condition, and the heating value of LTHR is high under high load condition. This leads to the changes of the starting crank angle of HTHR against engine load and it is a nuisance problem for the control of HCCI engine operation. Therefore, a fuel which exhibits the constant LTHR phasing against engine load would be preferable.

A supercharged 4-cylinder engine was introduced to evaluate how fuel properties affect engine combustion and performance in homogeneous charge compression ignition (HCCI) operation. In this study, choosing from 12 hydrocarbon constituents, model fuels were mixed to have the same distillation but different octane numbers (RON=70, 80, 92). For each fuel, RON distribution against distillation is same to keep the same octane number in cylinder vapor during the air-fuel compression process. To confirm the appropriateness of model fuels and test procedures, regular gasoline (RON=90) was also included. From the combustion analysis it was clear that the low temperature heat release depends on fuel characteristics. RON92 fuel has a small low temperature heat release, and a high temperature heat release combusts slowly.

The accuracy of the injection rate meter based on W. Zeuch's method in the measurement of multiple injection rate and amount was calibrated using a small cam driven piston that is driven by an electric motor. For the pre- or early-injection, a sensor with a high sensitivity can be applied to measure the small pressure increase due to the small injection amount. In case of the multiple injection that has the post and/or late injection, a pressure sensor with a low sensitivity must cover not only the large pressure increase due to the main injection but also the small pressure increase due to the post and/or late injection because the output of the high sensitivity sensor is saturated after the main injection. So the linearity of the low sensitivity pressure sensor was calibrated with the cam driven piston prior to the experiment with the actual injection system.

A fundamental examination was made of gasoline-fueled homogeneous charge compression ignition (HCCI) combustion under various compression ratios, intake temperatures and intake gas compositions. The results revealed the basic combustion characteristics, and the ignition timing and combustion duration were found for every set of conditions. Suitable intake air temperatures were also determined for every operating condition. Internal residual gas was used to raise the mixture temperature in the cylinder. The region of maximum engine speed was expanded without heating the intake air. Minimum and maximum indicated mean effective pressures (IMEP) were found in several engine speed regions under several residual gas rates. Based on the results, a comprehensive interpretation is given of conventional HCCI combustion in 2- and 4-stroke gasoline engines.

A gasoline-fueled homogeneous charge compression ignition (HCCI) engine with both direct fuel injection and negative valve overlap for exhaust gas retention was examined. The fuel was injected directly into the residual in-cylinder gas during the negative valve overlap interval for the purpose of reforming it by using the high temperature resulting from exhaust gas recompression. With this injection strategy, the HCCI combustion region was expanded dramatically without any increase in NOx emissions which were seen in the case of compression stroke injection. Injection timing during the negative valve overlap was found to be an important parameter that affects the HCCI region width. The injection timing also had the most suitable value in each engine load for the best fuel consumption. From this result, A new injection strategy in which only a portion of the fuel was injected during the negative valve overlap interval, while the rest of fuel was injected in intake stroke, was proposed.

This paper presents a study of antiknock performance under various octane numbers and compression ratios in a direct injection spark ignition (DISI) gasoline engine. The relationship between the octane number and engine performance in the DISI engine-the engine torque and the break specific fuel consumption (BSFC)-was investigated in comparison with a multipoint injection (MPI) engine. Due to the improvement in the charging efficiency and the advance of the ignition timing by cooled aspiration, the engine torque of the DISI engine was improved over that of the MPI engine. It was also found that the octane number requirement (ONR) was reduced. In addition, the possibility of engine performance enhancement at high compression ratios was studied. At high compression ratios, the engine torque is reduced due to the heavy knocking when low octane gasoline is used. However, an improvement in the engine torque has been observed with high octane gasoline.

The relation between the characteristics of a non-evaporating spray and those of a corresponding frame achieved in a rapid compression machine was investigated experimentally. The fuel injection pressure was changed in a range of 55 to 260 MPa and the other injection parameters such as orifice diameter and injection duration were changed systematically. The characteristics of the non-evaporating spray such as the Sauter mean diameter and the mean excess air ratio of the spray were measured by an image analysis technique. The time required for a pressure rise due to combustion was taken as an index to characterize the flame. It was concluded that the mean excess air ratio of a spray is the major factor which controls the burning rate and that the high injection pressure is effective in shortening the combustion duration and reducing soot formation.

The two-dimensional distribution of a soot cloud in an unsteady spray flame in a rapid compression machine(RCM) was visualized using the laser sheet scattering technique. A 40 mm x 50 mm cross section on the flame axis was illuminated by a thin laser sheet from a single pulsed Nd:YAG laser(wavelength 532 nm). Scattered light from soot particles was taken by a CCD camera via a high speed gated image intensifier. The temporal variation of the scattered light images were presented with the injection pressure as a parameter. The results showed that scattered light was intense near the periphery of the flame tip and that the scattered light becomes weaker significantly and disappears fast after the end of injection as injection pressure is increased. This technique was also applied to the visualization of the two-dimensional distribution of liquid droplets in the non-evaporating spray to correlate it with the soot concentration distribution.

An experimental evaluation of the reliability of the Zeuch's method was carried out. The following were derived: 1) cavitation limits the minimum back pressure available; 2) the injection rate measured by the Zeuch's method agrees with that by the W.Bosch's method; 3) the effect of dynamic pressure of the injected fuel jet has a negligible effect on the pressure sensor which is attached to the chamber wall; and 4) the high-frequency noise after the end of injection observed in the Zeuch's measurement can be effectively removed by either a low-pass filter or an inverse Fourier transform processing.