森吉 泰生

Thermocouples are widely used to measure the local gas temperature due to its accuracy and convenience. However, it is difficult to use thermocouples in a transient phenomenon such as reacting fields. In this study, the unsteady gas temperature inside a combustion chamber was measured by using an improved two-wire thermocouple technique. Based on previous two-wire methods, some modifications were examined. Firstly, numerical analysis of heat transfer between transient flow and thermocouple was performed to see what kind of modification was required. Secondly, a correction term was added to the basic equation, which was validated by experiments using a Rapid Compression and Expansion Machine. Finally, an improved two-wire thermocouple technique was evaluated by measuring the transient gas temperature inside a combustion chamber and compared to the estimated temperature using measured pressure data and assumptions of chemical equilibrium.

A newly developed small-sized IES (inductive energy storage) circuit with static induction thyristor at turn-off action was successfully applied to an ignition system. This IEC circuit can generate repetitive nanosecond pulse discharges. In this paper, the ignition system using repetitive nanosecond pulse discharges was investigated as an alternative to conventional spark ignition systems. The experiments were conducted using spherically expanding flame configuration for CH and C H -air mixtures under various conditions. In conclusions, the ignition system using repetitive nanosecond pulse discharges was found to extend lean flammability limits compared with conventional spark ignition systems. In addition, the ignition system using repetitive nanosecond pulse discharges could shorten ignition delay time. Copyright © 2008 SAE International. 4 3 8

In order to avoid knocking phenomena and also to reduce the cooling loss, the authors have studied a new piston-crank mechanism with various specifications. At first, numerical simulations to predict thermal efficiency and knocking limit were performed using 0-D model to confirm the idea. As a result, high compression ratio operation was found possible with a short combustion period. Next, a model engine was designed and built to evaluate the predicted result. A couple of leaf-shaped gears to move piston faster than usual engine near TDC was chosen to achieve higher thermal efficiency. Experimental results showed that higher indicated and brake thermal efficiency can be obtained and that lower exhaust gas emissions also can be obtained.

In this study, numerical simulation has been conducted for the spray injected from a slit nozzle injector for a direct gasoline engine. The droplets in the spray were investigated by the combination of Large Eddy Simulation (LES) and Lagrangian Discrete Droplet Model (DDM). Droplets are atomized through the primary breakup induced by the instability of the liquid surface and secondary breakup induced by relative velocity between droplet and surrounding gas. This paper applies three secondary breakup models to an injector spray flow and evaluates their results compared with experimental data.

Ships have many advantages in loading capacities compared with vehicles. If the amount of NOx can be reduced by some way, ships can be equipped with oxygen permeable membranes as an oxygen generator that has recently shown a remarkable improvement in the performance of producing more oxygen for the purpose of PM (Particulate Matter) reduction.<BR>Therefore, the objective of this study is to examine the effect of oxygen addition on exhaust gas emissions for marine diesel engines.<BR>In the experiment oxygen was added to the air suction pipe of a pre-combustion chamber type diesel engine. Then oxygen was added to the exhaust gas pipe before DPF (Diesel Particulate Filter) .<BR>The results were as follows:<BR>(1) Oxygen addition to the air suction pipe of a pre-combustion chamber type diesel engine decreases both ISF (Insoluble Organic Fraction) and SOF (Soluble Organic Fraction) . Oxygen addition works very well especially at all loads for reduction of ISF with an increase of 2% in oxygen concentration.<BR>(2) Although oxygen addition to the air suction pipe of a pre-combustion chamber type diesel engine increases NOx emission. The NOx emission of a pre-combustion chamber type diesel engine is not so much as that of a direct injection type engine. The increase of NOx emission is saturated with further increasing engine load.<BR>(3) DPF was effective even in an ordinary type engine that has mechanical fuel injection system and no supercharger. The reduction rate was superior in ISF compared to SOF.<BR>(4) Oxygen addition before DPF has almost no effect on PM reduction.

The phenomenon of autoignition is an important aspect of spark ignition engine's knock, hence reliable information on the relationship between the local gas temperature and the autoignition delay in a combustion chamber must be obtained to avoid knock. However, the measurement of local gas temperature, especially near the wall where knock occurs is difficult. A thermocouple is useful to measure local gas temperature even in the vicinity of wall. However, a conventional one-wire thermocouple is not adaptable to measure the in-cylinder gas temperature due to slow response. The issue of response can be overcome by adopting a twowire thermocouple. The two-wire thermocouple is consisted of two fine wire thermocouples with different diameter hence it is possible to determine the time constant using the raw data from each thermocouple. This technique was applied at more engine-like conditions, by developing a RCM (Rapid Compression Machine). Local gas temperature was measured in the combustion chamber near the wall under relatively strong and weak knock conditions. As a result, in the relatively strong knock condition, the heat release timing was found earlier and the temperature gradient neat the wall was steeper than of the weak knock condition.

In the previous study, the authors found that by moving the piston slowly around top dead center, degree of constant volume increased, but thermal efficiency was not improved due to increased heat loss. Consequently, direct injection stratified charge combustion was tested to selectively reduce heat loss, and an improvement of thermal efficiency was achieved at this time. Moreover, when pre-mixed spark ignition combustion is completed in a short time with quick burn, increasing the piston speed around top dead center rather than moving the piston slowly was found favourable to improve thermal efficiency.

In this study, the characteristics of diesel spray droplets, such as the velocity and the diameter were simultaneously measured by using an improved ILIDS (Interferometric Laser Imaging for Droplet Sizing) method on a 2D plane to evaluate the droplet breakup modeling. In numerical analysis, DDM (Discrete Droplet Model) was employed with sub-models such as droplet breakup, droplet drag force and turbulence. Experiments have been performed with an accumulator type unit-injector system and a constant-volume high-pressure vessel under the condition of quiescent ambient gas. The injection pressure and ambient gas pressure were set up to 100 MPa and 0.1 / 1 MPa, respectively. The nozzle orifice diameter was 0.244 mm with a single hole. The measurement region was chosen at 40 ∼ 60 mm from the nozzle-tip. Numerical analysis of diesel sprays was conducted and the results were compared to the measured results. A modification of TAB droplet breakup model was made by introducing statistically determined breakup time. As a result, the profile of droplet diameter distribution could be well predicted even in strongly unsteady regions compared to experimental results. Also, spray predictions under an engine-like condition were carried out. A plausible result was deduced using the modified breakup model compared to of the original breakup model. Copyright © 2007 Society of Automotive Engineers of Japan, Inc.

The characteristics of a diesel spray, such as the diameter, the velocity and the droplet distribution on a 2D plane were simultaneously measured by using an improved ILIDS (Interferometric Laser Imaging for Droplet Sizing) method. The experiments were performed with an accumulator type unit injector system and a constant-volume high-pressure vessel under the condition of quiescent ambient gas. The injection pressure and ambient gas pressure were set at 60/100 MPa and 0.1/1 MPa, respectively. The injection duration was set at 2ms, and measurements were made at 1.5ms after the end of injection. The orifice diameter of the injector used was 0.24mm with a single hole. The measurement was made at 40-60mm from the nozzle-tip. As a result, the correlations between the droplet size, the velocity and the spatial distribution were found under different injection and ambient gas pressures.

In reciprocating internal combustion engines, the Otto cycle indicates the best thermal efficiency under a given compression ratio. To achieve an ideal Otto cycle, combustion must take place instantaneously at top dead center, but in fact, this is impossible. Meanwhile, if we allow slower piston motion around top dead center, combustion will be promoted at that period; then both the in-cylinder pressure and degree of constant volume will increase, leading to higher thermal efficiency. In order to verify this hypothesis, an engine with slower piston motion around top dead center, using an ideal constant volume combustion engine, was built and tested. As anticipated, the degree of constant volume increased. However, thermal efficiency was not improved, due to increased heat loss. Accordingly more experiments, which achieved a slower piston motion around top dead center by adopting a larger ratio between the connecting-rod length and the crank radius, were carried out using direct injection stratified charge combustion, which allows selective reduction of heat loss. High thermal efficiency was attained, as expected. On the other hand, an engine with a faster piston motion around top dead center, created by decreasing the ratio between connecting-rod length and crank radius, attained high thermal efficiency with quick burn premixed spark ignition combustion.

In reciprocating internal combustion engines, Otto cycle indicates the best thermal efficiency under the same compression ratio. To achieve this, combustion must take place instantaneously at top dead center, but it is actually impossible. Meanwhile, if 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 slower piston motion by ideal constant volume comcustion was tested. It was revealed that the thermal efficiency could not be improved nevertheless an increase in degree of constant volume and lower pumping loss. Numerical.analysis deduced that increased heat loss cancelled out the effect of the higher degree of constant volume and that faster piston motion around top dead center rather achieves an improvement of thermal efficiency in a case where rapid combustion was realized.

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.

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. NO 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. © 2006 IOP Publishing Ltd. 2 +

Knock phenomenon in SI engines is regarded as an auto-ignition of unburned end-gas, and it has been widely examined by using rapid compression machines (RCM), shock-tubes or test engines. Recent researches point out the importance of the low temperature chemical reaction and the negative temperature coefficient (NTC). To investigate the effects, analyses of instantaneous local gas temperature, flow visualization and gaseous pressure were conducted in this study. As measurements using real engines are too difficult to analyze, the authors aimed to make measurements using a constant volume vessel under knock conditions where propagating flame exists during the induction time of auto-ignition. Adopting the two-wire thermocouple method enabled us to measure the instantaneous local gas temperature until the moment when the flame front passes by. High-speed images inside the unburned region were also recorded simultaneously using an endoscope. As a result, it was found that when knock occurs, the auto-ignition initiation time seems slightly early compared to the results without knock. This causes a higher volume ratio of unburned mixture and existence of many hot spots and stochastically leads to an initiation of knock. Copyright © 2006 by The Japan Society of Mechanical Engineers.

A new combustion method of high compression ratio SI engine was studied and proposed in order to achieve high thermal efficiency, comparable to that of CI engine. Compression ratio of SI engine is generally restricted by the knocking phenomena. A combustion chamber profile and a cranking mechanism were studied to avoid knocking with high compression ratio. Because 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 large heat loss, which may cancel the gain of higher compression ratio operation. Thereby, a special cranking mechanism was adapted which allowed the piston to move rapidly near TDC. Numerical simulations were performed to optimize the cranking mechanism for achieving high thermal efficiency. An elliptic gear system and a leaf-shape gear system were employed in numerical simulations. Livengood-Wu integral, which is widely used to judge knocking occurrence, was calculated to verify the effect for the new concept. As a result, this concept can be operated at compression ratio of fourteen using a regular gasoline. A new single cylinder engine with compression ratio of twelve and TGV (Tumble Generation Valve) to enhance the turbulence and combustion speed was designed and built for proving its performance. The test results verified the predictions. Thermal efficiency was improve over 10% with compression ratio of twelve compared to an original engine with compression ratio of ten when strong turbulence was generated using TGV, leading to a fast combustion speed and reduced heat loss. Copyright © 2006 KSAE.

Butt-welded fine gauge type-K thermocouples of three different diameters, 25, 50 and 100 μm, were produced according to an original method and used for gas and wall temperature measurement in an uncoated substrate so as to compare durability and detection performance. The results showed that 50 μm diameter thermocouples are suitable for this type of measurement, since these thermocouples have a response performance as quick as that of 25 μm thermocouples, and because of excellent toughness. Composition analysis of the produced thermocouples also showed that poor mixture of alumel and chromel was responsible for the weakness of 25 μm thermocouples. © 2006 Society of Automotive Engineers of Japan, Inc. All rights reserved.

The authors have performed experiments on compression-ignition (CI) for a single-cylinder Schnurle-type two-stroke gasoline direct injection (DI) engine which employs a variable exhaust port, area, and deduced two presumptions from the experimental results. Firstly, the spatial distributions of fuel concentration and in-cylinder gas temperature are indispensable to enable CI operation under stratified charge conditions, because CI operation is not possible in a DI system although the necessary conditions of the scavenging efficiency and the in-cylinder gas temperature for the initiation of CI in homogeneous charge conditions are satisfied. Secondly, it is possible that flame propagation occurs in stratified charge CI conditions, because the combustion period in the later stage after 80% mass burned becomes longer than that with homogeneous charge CI combustion. In this report, in order to verify the above two presumptions deduced from experiments, the gas exchange process and mixture formation process were numerically analyzed, and the initiation conditions of CI were estimated using a CHEMKIN application. As a result, in case of CI with a late injection timing in DI system, it was found that CI was possible because high temperature but no fuel region and low temperature but rich fuel region exist in the cylinder due to inhomogeneous spatial distributions of fuel and temperature. Also, in case of CI with a late injection timing, the flame propagation was possible in the low-temperature and diluted rich region. Thereby, the two presumptions deduced from the experimental results were validated from the numerical analysis results. Copyright © 2006 by The Japan Society of Mechanical Engineers.

In this study, the characteristics of Diesel spray droplets, such as the velocity, the diameter and the droplet distribution were simultaneously measured by using an improved ILIDS (Interferometric Laser Imaging for Droplet Sizing) method. In numerical analysis, DDM (Discrete Droplet Model)·· model, which is used to calculate the diesel spray was employed. The experiments have been performed with an accumulator type unit injector system and a constant-volume high-pressure vessel under the condition of quiescent ambient gas. The injection pressure and ambient gas pressure were set up to 100 MPa and 0.1/1 MPa, respectively. Injection duration was set at 2 ms and, measurements were made at 1.5 ms after the end of injection. The nozzle orifice diameter was 0.244 mm with single hole. The measurement region was chosen at 40-60 mm from the nozzle-tip. In addition, numerical analysis of diesel sprays was conducted and the results were compared to the measured results. In numerical analysis, calculation of the spray by DDM was carried out to examine the droplets breakup process and to evaluate the breakup modeling. Also, in order to achieve more accurate predictions, investigations and modifications of sub-models and initial boundary conditions have been carried out.

The phenomenon of autoignition is an important aspect of HCCI and knock, hence reliable information on local gas temperature in a combustion chamber must be obtained. Recently, several studies have been conducted by using laser techniques such as CARS. It has a high spatial resolution, but has proven difficult to apply in the vicinity of combustion chamber wall and requires special measurement skills. Meanwhile, a thermocouple is useful to measure local gas temperature even in the vicinity of wall. However, a traditional one-wire thermocouple is not adaptable to measure the in-cylinder gas temperature due to slow response. The issue of response can be overcome by adopting a two-wire thermocouple. The two-wire thermocouple is consisted of two fine wire thermocouples with different diameter hence it is possible to determine the time constant using the raw data from each thermocouple. In this study, measurements such as local gas temperature inside a constant-volume combustion chamber, pressure and visualization were achieved with and without autoignition. The relationship between the ignition delay and the gas temperature was clarified. This is a very important result to analyze the knock phenomenon. As a result, negative temperature coefficient was found to mostly affect autoignition in this experimental condition. This technique was applied at more engine-like conditions, by developing a new RCM (Rapid Compression Machine). In preliminary tests, local gas temperature inside the combustion chamber under compression without combustion was measured to examine the accuracy of two-wire thermocouple. Copyright © 2006 SAE International.

Thermocouples are widely used to measure gas temperature due to its accuracy and convenience. However, it is difficult to employ thermocouples in a transient phenomena such as reacting fields. In this study, the unsteady gas temperature inside a combustion chamber was measured by using an improved two-wire thermocouple technique. Based on previous two-wire methods, some modifications were examined. Firstly, numerical analysis of heat transfer between transient flow and thermocouple was performed to see what kind of modification is required. Secondly, a correction term was added to the basic equation, which was validated by experiments using RCEM. Finally, an improved two-wire thermocouple technique was evaluated by measuring the transient gas temperature inside a combustion chamber comparing to the estimated temperature using measured pressure data and assumptions such as chemical equilibrium to see the adaptability of this technique.

A new combustion method of high compression ratio SI engine was studied and proposed in order to achieve higher thermal efficiency of SI engine comparable to that of CI engine. Compression ratio of SI 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. Copyright © 2005 SAE International.

In order to improve thermal efficiency of spark ignition engines, the authors have studied means to improve degree of constant volume. The ideal Otto cycle realizes the maximal degree of constant volume with an instantaneous combustion at TDC. However, it is actually impossible to achieve instantaneous combustion as the combustion speed is limited. Thereby, the authors thought of an idea to increase degree of constant volume. That is to make the piston speed slow during combustion period by active piston-movement control, allowing more time for combustion. As a result, degree of constant volume was improved, but indicated thermal efficiency, estimated by integrating P-V diagram, was deteriorated. A longer expansion stroke was found to keep a longer period of high temperature and then, heat loss increased, leading to a decrease in indicated work. In this study, the authors built another test engine that has equal strokes of compression and expansion but has a slow piston speed in the first half of expansion stroke by making the length of connecting-rod extremely long and made some tests. In the previous report, because the numerical calculation predicted that the shorter the combustion period becomes, the worse the thermal efficiency does, a direct fuel injection system was employed to take a longer combustion period and a different profile of heat release rate compared to the port injection system. As a result, thermal efficiency did not depend on the length of connecting-rod very much, and the numerical simulation predicted the same tendency as experiment, depending on the profile of heat release rate. Copyright © 2005 Society of Automotive Engineers of Japan, Inc. and Copyright © 2005 SAE International.

A new combustion method of high compression ratio SI engine was studied and proposed in order to achieve higher thermal efficiency of SI engine comparable to that of CI engine. Compression ratio of SI 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. Copyright © 2005 SAE International.

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 degree of constant volume.

In order to improve thermal efficiency of spark ignition engines, a novel method to increase degree of constant volume was considered. Because the combustion speed is not infinity as assumed in Otto cycle but limited, it is necessary to decrease the piston-movement around TDC so as to increase degree of constant volume. At first, experimental study was made to confirm this. A test engine which has longer expansion stroke than compression stroke and enables a slow piston-movement during combustion period was built. The experimental data indicated an increase in degree of constant volume, but did not show an increase in thermal efficiency. In order to clarify this reason, numerical simulations are conducted in this paper. As a result, the gain due to the increase in degree of constant volume caused by piston-motion during combustion was found not exceeding the loss by increased heat loss. Numerical analysis deduced that increasing the piston-movement near TDC rather achieve an improvement of thermal efficiency in case that a rapid combustion was realized.

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.

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.