Yasuo Moriyoshi

Extension of an operating load range of a four-cylinder gasoline homogeneous charge compression ignition engine via a blowdown supercharge system, aiming at in-cylinder thermal stratification

In order to extend the operational range with a gasoline fueled multi-cylinder homogeneous charge compression ignition engine, a blowdown supercharge system and an exhaust gas recirculation guide was developed. The concept was to provide a large amount of diluted mixture and a strong in-cylinder thermal stratification for decreasing nitrogen oxide emissions and pressure rise rate during high-load homogeneous charge compression ignition operation. Secondary air injection was also proposed to reduce a cylinder-to-cylinder variation in ignition timing, which is one of the limiting factors of multi-cylinder homogeneous charge compression ignition operation. In advance of experimental works, the blowdown supercharge system and the exhaust gas recirculation guide were proved to be effective to reduce pressure rise rate for high-load operation using three-dimensional in-cylinder flow simulations and zero-dimensional multi-zone simulations with detailed chemical kinetics. Based on the simulation results, experiments were conducted using a slightly modified production four-cylinder gasoline engine. At first, the effects of the proposed techniques were experimentally investigated by focusing on one cylinder out of four. Then, a four-cylinder homogeneous charge compression ignition operation test using the new techniques was carried out. The one-cylinder measurements revealed that the blowdown supercharge system with an exhaust gas recirculation guide is capable of extending the homogeneous charge compression ignition operating range up to a net indicated mean effective pressure of 590 kPa for naturally aspirated conditions. In addition, secondary air injection was experimentally demonstrated as a technique for reducing a cylinder-to-cylinder variation in ignition timing. Reducing the cylinder-to-cylinder variation in ignition timing, four-cylinder homogeneous charge compression ignition operation with a net indicated mean effective pressure of 570 kPa was successfully achieved with the blowdown supercharge system and the exhaust gas recirculation guide.

Enhancement of ignition characteristics of lean premixed hydrocarbon–air mixtures by repetitive pulse discharges

Abstract A newly developed small-sized inductive energy storage (IES) circuit that uses a semiconductor switch for the turn-off action is successfully applied to an ignition system in spark ignition engines operating under lean fuel–air ratios. This IES circuit can generate repetitive nanosecond pulse discharges. Experiments are conducted by means of a spherically expanding flame configuration for C3H8–air mixtures under various conditions. Findings show the investigated ignition system improves the inflammability of lean combustible mixtures in terms of extended flammability limits, shorted ignition delay time, and extended dilution limits, compared with conventional spark ignition systems.

Experimentally Evaluated Spray Model for a Swirl-Type Injector

To clarify the fuel spray formation process for a swirltype injector, numerical analyses using both VOF (Volume Of Fluid) model and DDM (Discrete Droplet Model) method are carried out. VOF model is used to simulate the two-phase flow inside the injector and also the liquid film formation process outside the nozzle, while DDM is used to simulate a free fuel spray in a constant-volume chamber using initial conditions deduced by empirical equations or calculated results of VOF model. As a result, fairly good agreement of spray characteristics, such as the spray shape and the tip penetration between the experiment and calculation can be obtained by adopting initial conditions calculated by VOF model. However, improvements of droplet breakup models and of two-phase flow calculation method would be required to achieve quantitatively good agreement.

Improvement of thermal efficiency of a four-cylinder gasoline homogeneous charge compression ignition engine via blowdown supercharging

The objective of this study is to develop a practical technique to achieve homogeneous charge compression ignition operation with a wide operating range using a blowdown supercharge system, which has been previously demonstrated as an effective technique to extend the upper load limit of acceptable homogeneous charge compression ignition operation. The valve actuation strategy to attain acceptable homogeneous charge compression ignition operation in a wide operating range has been newly developed and experimentally examined. The proposed strategy provides high in-cylinder temperature and a relatively small amount of in-cylinder mixture during low-load operations to improve the combustion stability while providing a large amount of diluted mixture for high-load operations to keep the in-cylinder pressure rise rate and nitrogen oxide emissions low. In addition, thermal efficiency and exhaust emissions for various homogeneous charge compression ignition operating loads using the blowdown supercharge system were experimentally investigated. Experimental results showed that the proposed valve actuation strategy, in which early intake valve closing and relatively late exhaust gas recirculation valve opening occurred, was effective to increase combustion stability during low-load conditions, and a stable homogeneous charge compression ignition operation at a net indicated mean effective pressure of 140 kPa was achieved. Compared to conventional spark-ignition operation, 14% to 35% improvement in brake specific fuel consumption rate was attained with more than 99% reduction in nitrogen oxide emissions for homogeneous charge compression ignition operation using the blowdown supercharge system.

Effect of the Ratio Between Connecting-rod Length and Crank Radius on Thermal Efficiency

In reciprocating internal combustion engines, Otto cycle indicates the best thermal efficiency under the same compression ratio among ideal cycles. To achieve this, combustion must take place instantaneously at top dead center, but it is actually impossible. Meanwhile, if a slower piston motion around top dead center was allowed, both the in-cylinder pressure and degree of constant volume would increase, leading to higher thermal efficiency. In order to verify this idea, an engine with a slow piston motion by adopting a large ratio between the connecting-rod length and the crank radius was tested. As expected, while degree of constant volume was increased, thermal efficiency was not improved due to increased heat loss. Further experiments were carried out using a direct injection stratified charge combustion system which allows selective reduction of heat loss, and high thermal efficiency was attained. On the contrary, an engine with a faster piston motion by adopting a smaller ratio between the connecting-rod length and the crank radius attained high thermal efficiency under the quick burn pre-mixed spark ignition combustion.

A Study on New Combustion Method of High Compression Ratio Spark Ignition Engine

A new combustion method of high compression ratio Sl engine was studied and proposed in order to achieve higher thermal efficiency of Sl engine comparable to that of Cl engine. Compression ratio of Sl engine is generally restricted by the knocking phenomena. A combustion chamber profile and a cranking mechanism are studied to avoid knocking with high compression ratio. Since reducing the end-gas temperature will suppress knocking, a combustion chamber was considered to have a wide surface at the end-gas region. However, wide surface will lead to high heat loss, which may cancel the gain of higher compression ratio operation. Thereby, a special cranking mechanism was adopted which allowed the piston to move rapidly near TDC. Numerical simulations were performed to optimize the cranking mechanism for achieving higher thermal efficiency. An elliptic gear system and a leaf-shape gear system were employed in the simulations. A knocking index number was calculated to verify the effect for the new concept. As a result, this concept can be operated at the compression ratio of 14 using regular gasoline. A new single cylinder engine was designed and built for proving its performance. The experimental results show that a knocking limit has apparently improved and better indicated thermal efficiency has been obtained. Finally the indicated thermal efficiency has improved approximately 8% in the limited condition in the case of compression ratio of 12 by realizing this concept.

Analysis of compression ignition combustion in a schnurle-type gasoline engine comparison of performance between direct injection and port injection systems-

A two-stroke Schnurle-type gasoline engine was modified to enable compression-ignition in both the port fuel injection and the in-cylinder direct injection. Using the engine, examinations of compression-ignition operation and engine performance tests were carried out. The amount of the residual gas and the in-cylinder mixture conditions were controlled by varying the valve angle rate of the exhaust valve (VAR) and the injection timing for direct injection conditions. It was found that the direct injection system is superior to the port injection system in terms of exhaust gas emissions and thermal efficiency, and that almost the same operational region of compression-ignition at medium speeds and loads was attained. Some interesting combustion characteristics, such as a shorter combustion period in higher engine speed conditions, and factors for the onset of compression-ignition were also examined.

Quasi 2-D Measurements of Gaseous and Liquid Fuel Concentrations Using Two-Color Laser Beam Scanning Technique

Planer Laser Induced Fluorescence (PLIF) has been employed to measure the spatial liquid and vapor fuel concentration distributions, although it is generally difficult to achieve quantitatively accurate measurement. The authors devised a 2-D fuel spray concentration distribution measurement method which combines three optical principles; absorption, fluorescence, and scatter. NO2 gas was used as a fluorescence dopant while Ar+ laser was employed as a light source by scanning across the cylinder in order to measure the spatial fuel concentration distribution. This technique was applied to gaseous jets and swirl sprays. Quantitative measurement was successfully achieved in both tests. Also, the characteristics of liquid and vapor fuel concentration distribution using a swirl type injector were confirmed.

2-D Quantitative Measurement of Fuel Jet Concentration Using Laser-Beam-Scanning Method

In order to measure the fuel jet concentration quantitatively, a technique combining methods of fluorescence with absorbance was developed. LIF method can estimate the spatial fuel distribution qualitatively, but quantitative measurement is difficult. Meanwhile, absorbance method can quantitatively obtain the integrated concentration on the light-path. Thereby, a combination of this technique and laser-beam-scanning technique enables us to measure the quasi 2-D fuel concentration quantitatively. In this study, this measurement method was applied to fuel jet fields in a constant volume bomb. As a result, quasi 2-D measurements of gas concentration were successfully attained by adopting some compensation techniques.

A Trial of Improving Thermal Efficiency by Active Piston Control -Speed Control Effect of Combustion Chamber Volume Variation on Thermal Efficiency-

In reciprocating internal combustion engines, the piston stops in a moment at top dead center (TDC), so there exists a necessary time to proceed combustion. However more slowing piston motion around TDC, does it have a possibility to produce the following effects? The slowed piston motion may expedite combustion proceed and increase cylinder pressure. This may lead to an increase of degree of constant volume. As a result, thermal efficiency may be improved. In order to verify this idea, two types of engines were tested. The first engine attained high cylinder pressure as expected. The P-V diagram formed an almost ideal Otto cycle. However, this did not contribute to the improvement in the thermal efficiency. Then the second engine with further slower piston motion by active piston control was tested in order to examine the above reason. It was revealed that the increased heat loss cancelled out all other favorable features such as lower pumping loss and increase in dearee of constant volume.