Based on a 1.3L MPI turbocharged gasoline engine with high and low pressure EGR system, correlation between ion current signal phase and ignition timing under declared operating condition has been studied. The results show that higher EGR rate needs to cooperate more advanced ignition timing, which leads to advanced ion current signal phase. Both under high and low pressure EGR condition, correlation coefficient between ion current signal phase and ignition timing is over 0.7, including 75% experiment points is over 0.9, so ion current signal phase is able to estimate ignition timing. Base on this, an online monitoring and feedback control strategy of ignition timing is proposed, which is employed to record the times of actual ignition timing deviating from ideal ignition timing and adjust ignition timing. The average accuracy rate of online monitoring function is 97.2%. This strategy can help to judge whether the engine operates properly and avoid adverse consequences caused by inaccurate matching of ignition timing and EGR rate.

We measured the vibrational and rotational temperatures in a spark ignition plasma by using optical emission spectroscopy, and investigated the influence of the air flow and atmospheric pressure on these temperatures. The optical emissions from the plasma were led to an imaging spectroscope through an optical fiber. The temperature was regulated by fitting a theoretically calculated spectrum to an experimentally measured spectrum, which was formed by nitrogen molecule emission from 372 nm to 382 nm. We examined the spark discharge plasma with a flow of atmospheric air at a discharge energy of 80 mJ. The air flow caused the spark discharge channel to elongate downstream. At the center of the spark plug gap, the vibrational temperature in the plasma was 4000 K, while the rotational temperature was 2000 K. This plasma can be regarded as being in non-thermal equilibrium, because the vibrational temperature was higher than the rotational temperature. Near a position 3 mm downstream from the spark plug gap, the vibrational and rotational temperatures increased to 4500 K and 4000 K, respectively, while approaching each other. Both temperatures reached a maximum value. These results show that the plasma transits from non-thermal equilibrium to thermal equilibrium as it is elongated by the air flow. Ignition efficiency improvements can be expected if the time required to transition from non-thermal to thermal equilibrium can be shortened.

Gasoline Partially Premixed Combustion (PPC) is a promising alternative combustion concept that can offer both high indicated efficiency and low exhaust emissions in terms of NOx and soot, compared to conventional diesel combustion (CDC). Previous research has shown that PPC can operate with gasoline-like fuels of varying RON numbers. Some of the most promising results come with the use of gasoline of low octane number, around RON 70. In this study, a commercially available; 2 litre Euro 6 light duty diesel engine is being operated under various load and speed conditions with the use of RON 75 gasoline. The aim is to evaluate the ability of the engine to operate under PPC conditions with the use of as much OEM hardware installed as possible, in this case a double stage turbocharger. High amount of EGR, approximately 30%, is used in order to control NOx production and combustion reaction rates, together with a double injection strategy, which is beneficial at controlling the pressure rise rate and enable high load operation. The engine is operated at three different RPM levels, 1200-1800-2400 and between 2 to 16 bar IMEPg. Results show that combustion instability poses the limit at the low load while low oxygen content restricts the high load operation. Due to the premixed type of combustion, a fast combustion event is possible, giving a higher effective expansion ratio, which improves the indicated efficiency to levels higher than CDC, while indicated emissions are comparable to CDC operation.

Gasoline partially premixed combustion (PPC) is a promising combustion concept with high indicated thermodynamic efficiency (ITE) and low emission level. This study investigated the effect of gasoline viscosity index improvement on the multi-cylinder engine performance and the dependence of the PPC combustion on injection pressure over a wide range of engine speeds and loads. Results show that a small amount of viscosity improver can improve the viscosity of gasoline effectively without influencing the octane numbers. This is beneficial for elevating the mechanical efficiency of the fuel pump and improving the brake thermal efficiency (BTE) of the engine. For the part and medium load conditions, the requirement of common-rail pressure in PPC mode with engine-out NOx and soot emissions below Euro 6 levels is significantly lower than the calibration of conventional diesel combustion (CDC) mode with tailpipe Euro 6 emissions. For the high-load conditions, the low-speed operations are prone to achieve high premixing. While the high-speed operations are mainly mixing-controlled with similar NOx-soot trade-off relationship compared to CDC mode under moderate injection pressures. The fuel injection pressure becomes the most important driving factor for air-fuel mixing in PPC mode. The local equivalence ratio dominated by the injection pressure is more important than the global equivalence ratio for soot reductions. As a result, gasoline PPC load extension is very sensitive to rail pressure, and its injection pressure requirement is much higher than that of the Euro 6 CDC mode.

This study investigated the transition from conventional Compression Ignition (CI) to Partially Premixed Combustion (PPC) in an optical engine for fuels with differing properties. Combustion stratification and emissions were measured with diesel, naphtha and their corresponding surrogate fuels, N-heptane and PRF50. The aim of the study is to link the combustion images with engine out emissions and mixture homogeneity. Single injection strategy with the change of start of injection (SOI) from late to early injections was employed. Results show that combustion phasing trend is similar for diesel/N-heptane as well as for naphtha/PRF50 as the SOI moved from late injection timing to early injection timing. However, there is a significant difference in combustion phasing behavior for gasoline like fuels (naphtha and PRF50) and diesel fuels (diesel and N-heptane). CO emissions show an inverted V-shaped trend with one single peak in the transition zone. A “W” shape trend, with two bottoms at various dilution rates is observed for the UHC emissions. NOX emissions are high in the transition zone and decreased to lower levels in CI and PPC zones. NOX emissions are significantly reduced by reducing the intake O₂ concentration with nitrogen. Except for diesel, the other three fuels show lower soot emissions. When compared to diesel like fuels, the natural luminosity of the images are lower for gasoline like fuels, indicating better premixed combustion. As the SOI is changed from CI to PPC mode, the combustion stratification increases towards a peak value in the transition zone and then decreases to a low level in PPC zone. A competition exists between the intake temperature and the dilution rate for the combustion stratification. The level of stratification is higher for real fuels (diesel and naphtha) when compared to surrogate fuel (N-heptane and PRF50).

The reactivity controlled compression ignition (RCCI) concept has the potential to make combustion cleaner and more efficient. This paper describes studies on RCCI combustion using natural gas (NG) and diesel as high-octane and highcetane fuels, respectively. The purpose of this study is to investigate the influence of late inlet valve closing on NG-diesel RCCI combustion. Experimental results reveal that indicated thermal efficiencies over 50% were achieved for most NG-diesel RCCI combustion cases at various inlet valve closing (IVC) timings. RCCI combustion also achieved ultra-low NOx and soot emissions, albeit at the cost of high UHC and CO emissions. Numerical work was also conducted to explore NG-diesel RCCI combustion details.

The present study describes the applicability of a surface modification process developed on the basis of mechanical methods, to the sliding interfaces of engine components such as piston skirts. The developed process consisted of a micro shot peening and a roller burnishing. A solid lubricant, such as molybdenum disulfide (MoS2), was supplied into the micro dimples formed by the shot peening, and was then made to penetrate by means of the roller burnishing. The resulting surface was flat and consisted of a densely penetrated MoS2 phase and a truncated substrate. The surface modification process was applied to an aluminum cast alloy (AC8A). The tribological properties were evaluated using a ring-on-disc-type testing apparatus under lubricated conditions using a cast iron (FC230) ring as a mating specimen. The friction coefficient of the modified surface was low and stable. In addition, a tin (Sn) coating applied to the AC8A surface in advance of the roller burnishing was an effective way to increase the adhesion strength of the MoS2. A similar surface modification was applied to a piston skirt and was evaluated under firing conditions. It was confirmed that the application of the surface modification was an effective way to decrease the friction loss of the piston skirt. Furthermore, the multiplied effects of the surface modification and a surface texture fabricated using an interrupted micro cutting process were also evaluated.

Improvement in thermal efficiency of internal combustion engines has been required, and reduction of the mechanical friction loss is also required for with reduction of the cooling loss or the exhaust loss. This paper was described the structure of the floating liner type piston friction engine used by this research, the method of running-in and setup method of the zero point of measurement data. Furthermore, frictional force was measured using the piston penetrated solid lubricant with surface plastic flow process surface modification, the plateau liner and low viscosity oil, and verified the possibility that there was about 30 to 40% of friction reduction effect.

In order to reduce CO2 emissions and fuel consumption, the reduction of mechanical friction loss is very important technologies. To reduce such friction loss, understanding the lubrication conditions of engine sliding surfaces are very important. In order to investigate their conditions and to validate the CAE (Computer aided engineering), the author has developed a thin-film pressure sensor for measuring oil-film pressure distributions in engine bearings, piston skirts, pinbosses. However, the lubrication condition of the engine has become strict year by year, and it became necessary to develop a high durability thin film pressure sensor. For deformation, we developed "Multi-layer type oil film pressure sensor". Also, with regard to durability, by optimizing DLC for thin film sensor, we have made it possible to accurately measure oil film pressure in the engine.

In this study, a new method for visualization of oil film flow is proposed and the validity of this method is experimentally confirmed. The proposed method is to visualize the oil film by dissolving a photochromic dye in lubricating oil and coloring with UV rays. This paper explains the basic study of photochromic reaction and the application to flow visualization. Firstly, we quantified the color density of colored solution by applying the absorbance calculated from images before and after coloring. As a result, it was confirmed that the color density was quantified and also oil film thickness can be measured from the absorbance. Secondly, the characteristics of coloring and fading reaction were examined. Consequently, it was confirmed that the increasing energy density of UV rays is effective in improving color density and the optimal energy density of UV rays can be acquired from the model formula of coloring reaction. We also measured the color fading reaction under the different temperature conditions and confirmed the temperature dependence of the solution of Spiropyran and Ester-based oil from an Arrhenius plot. Finally, flow visualization was tried in the complex shape flow channel of approximately ten micrometers in thickness. The test oil flowing through this channel was colored with a focused third harmonic of YAG laser. The distributions of flow velocity and supplied oil to the channel were visualized with this method and confirmed the validity of proposed method.