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An author's previous studies addressed a combustion system which reduces emissions, noise, and fuel consumption by using PCCI with the split injection of fuel. This concept relies on the premixed combustion of the first injected fuel and accelerated oxidation by the second injected fuel. Although this combustion system requires the optimization of the timing of the second injection, the details of how noise and emissions are reduced have not been elucidated. In this paper, the authors explain the mechanism whereby emissions and noise are reduced by the second injection. In-cylinder visualizations and numerical simulations both showed an increase in smoke and CO as the second injection timing was advanced, as induced by the inhibited oxidation of the rich flame. When the second injection timing is excessively retarded, the amount of soot forming around the near-nozzle increased.

The backward flow of the hot burned gas surrounding a diesel flame was found to be one of the factors dominating the set-off length (also called the lift-off length), that is, the distance from a nozzle exit into which a diffusion flame cannot intrude. In the combustion chamber of an actual diesel engine, the entrainment of the surrounding gas into a spray jet from a multi-hole nozzle is restricted by the walls and adjacent spray jets, which induces the backward flow of the surrounding gas. A new momentum theory to calculate the backward flow velocity was established by extending Wakuri's momentum theory. Shadowgraph imaging in an optical engine successfully visualized the backward flow of the hot burned gas.

A novel diagnostic technique named a “Tracer-Producing LIF technique” which enables 2-dimensional measurement of an internal EGR within an engine cylinder, has been developed. The main feature of this technique is the utilization of a fuel additive that does not itself emit an LIF signal by irradiation of UV-light but whose combustion products radiate strong LIF emissions by UV-light irradiation. Internal EGR behaviors can be measured by observing LIF images that are excited by a UV-laser sheet. Firstly, principles of this technique were confirmed and fuel additives were selected. Then, the “Tracer-Producing LIF technique” was applied to an optically accessible single-cylinder gasoline engine in which the entire pent-roof area can be observed from the side of the engine. The internal EGR behaviors were measured through the entire engine cycle, from intake to exhaust.

Over the last few decades, in-cylinder visualization using optically accessible engines has been an important tool in the detailed analysis of the in-cylinder phenomena of internal combustion engines. However, most current optically accessible engines are recognized as being limited in terms of their speed and load, because of the fragility of certain components such as the elongated pistons and transparent windows. To overcome these speed and load limits, we developed a new generation of optically accessible engines which extends the operating range up to speeds of 6000 rpm for the SI engine version, and up to in-cylinder pressures of 20 MPa for the CI engine version. The main reason for the speed limitation is the vibration caused by the inertia force arising from the heavy elongated piston, which increases with the square of the engine speed.

This paper describes a laser-induced fluorescence (LIF) method for quantitative 2-D fuel concentration measurements in an SI engine. The combination of fluorescence tracer and excitation wavelength to lower the temperature and pressure effects on LIF intensity were evaluated. Each kind of fluorescence tracer selected from ketones, aldehydes and aromatics has been excited at 248 nm or 266 nm in a heated and pressurized constant volume vessel. For the promising candidates, further evaluation has been performed using a fired visualization engine. The results show that the optimum combination which gives the lowest effects of temperature and pressure on LIF intensity is acetone with 266 nm excitation. 3-pentanone, which is commonly used fluorescence tracer has been shown to be not suitable for the quantitative measurements, especially in a fired engine.

NO laser-induced fluorescence (LIF) imaging and quantitative fuel distribution measurements in aport-fuel-injected 4-valve stratified-charge single-cylinder SI engine have been conducted using a tunable KrF excimer laser. The correlations between NO formation region and fuel distribution have been investigated for the horizontal stratification realized by fuel (iso-octane) injection in only one intake port. The NO LIF intensity is proportional to the exhaust NOx emissions. The strong NO LIF intensity region in expansion stroke corresponds to the location of the region with equivalence ratio (ϕ) between 0.8 and 1.1 in the stratified fuel distributions at spark timing. The exhaust NOx concentration is proportional to the area of region with ϕ =0.8 - 1.1.

To improve the thermal efficiency of an internal combustion engine, the application of ceramics to heat loss reduction in the cylinders has been studied [1-2]. The approach taken has focused on the low heat conductivity and high heat resistance of the ceramic. However, since the heat capacity of the ceramic is so large, there is a problem in that the wall temperature increases during the combustion cycle. This leads to a decrease in the charging efficiency, as well as knocking in gasoline engines. To overcome these problems, the application of thermal insulation without raising the gas temperature during the intake stroke has been proposed [3-4]. As a means of achieving this, we developed a "temperature swing heat insulation coating" [5, 6, 7, 8, 9]. This reduces the heat flux from the combustion chamber into the cooling water by making the wall temperature follow the gas temperature as much as possible during the expansion and exhaust strokes.

Two-line excitation LIF (Laser-Induced Fluorescence) technique for 2-dimensional temperature measurements in an engine cylinder before ignition is presented. From the fundamental examinations, the combination of toluene tracer with a pair of excitation lines of 248nm and 266nm has been selected because of the high LIF intensity ratio and closer excitation wavelengths. In-cylinder thermometry is conducted using a visualized single cylinder spark ignition engine both in PFI (port-fuel-injection) and DI (direct-injection) operation. The accuracy of this technique is determined through the homogeneous PFI experiment. Temperature and fuel distribution in unburned mixture are measured simultaneously in DI operation. It exists a strong correlation between equivalence ratio and temperature inside the mixture. Temperature in the fuel rich region is lower than in the fuel lean region.

Combustion of premixed lean mixture which arises from multi-point ignition is very promising and necessary for achieving both higher efficiency and lower nitrogen oxide (NOx) emission. A Premixed-Charge Compression Ignition (PCCI) engine has been manufactured experimentally and evaluated in terms of fuel economy and NOx reduction. The PCCI engine manufactured is a single cylinder engine with inlet port injection of gasoline, and has a compression ratio of 17.4. The PCCI engine operates stably in the air-fuel ratio range of 33-44. In the PCCI engine, spontaneous ignition occurs at unspecified points as it does in diesel engines. The flame then develops rapidly throughout the combustion chamber. Under conditions of stable combustion, the PCCI engine achieves equivalent fuel economy and much lower NOx emission compared with diesel engines. Furthermore, the effects of intake air heating and supercharging on extending the range of stable combustion have been examined.

The set-off length (also referred to as the “lift-off length”) is reduced by the re-entrainment of the burned gas by the backward flow surrounding a diesel spray jet produced by a multi-hole nozzle. In the present study, to estimate the equivalence ratio at the set-off length, a means of estimating the amount of burned gas that is re-entrained into the near-nozzle region of the diesel spray jet was established. The results revealed that the suppression of soot formation in quasi-steady diesel spray flames produced by a multi-hole nozzle and a high injection pressure is not attained by reducing the equivalence ratio at the set-off length. Analysis of the amount of soot along the spray axis using a two-color method revealed that the maximum soot amount position appears in a quasi-steady spray flame, after the collapse of the head vortex in which a dense soot cloud is formed. The maximum soot amount position does not change even if the injection pressure varies.