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Journal Article

Extension of Operating Range of a Multi-Cylinder Gasoline HCCI Engine using the Blowdown Supercharging System

2011-04-12
2011-01-0896
The objective of this study is to develop a practical technique to achieve HCCI operation with wide operation range. To attain this objective, the authors previously proposed the blowdown supercharge (BDSC) system and demonstrated the potential of the BDSC system to extend the high load HCCI operational limit. In this study, experimental works were conducted with focusing on improvement of combustion stability at low load operation and the reduction in cylinder to cylinder variation in ignition timing of multi-cylinder HCCI operation using the BDSC system. The experiments were conducted using a slightly modified production four-cylinder gasoline engine with compression ratio of about 12 at constant engine speed of 1500 rpm. The test fuel used was commercial gasoline which has RON of 91. To improve combustion stability at low load operation, the valve actuation strategy for the BDSC system was newly proposed and experimentally examined.
Technical Paper

Extension of Lean and Diluted Combustion Stability Limits by Using Repetitive Pulse Discharges

2010-04-12
2010-01-0173
A newly developed small-sized IES (inductive energy storage) circuit with a semiconductor switch at turn-off action was successfully applied to an ignition system. This IES circuit can generate repetitive nanosecond pulse discharges. An ignition system using repetitive nanosecond pulse discharges was investigated as an alternative to conventional spark ignition systems in the previous papers. Experiments were conducted using constant volume chamber for CH₄ and C₃H₈-air mixtures. The ignition system using repetitive nanosecond pulse discharges was found to improve the inflammability of lean combustible mixtures, such as extended flammability limits, shorted ignition delay time, with increasing the number of pulses for CH₄ and C₃H₈-air mixtures under various conditions. The mechanisms for improving the inflammability were discussed and the effectiveness of IES circuit under EGR condition was also verified.
Journal Article

Very Lean and Diluted SI Combustion Using a Novel Ignition System with Repetitive Pulse Discharges

2009-11-03
2009-32-0119
A newly developed small-sized IES (inductive energy storage) circuit with semiconductor switch at turn-off action is successfully applied to an ignition system of a small gasoline internal combustion engine. This IES circuit can generate repetitive nanosecond pulse discharges. An ignition system using repetitive nanosecond pulse discharges is investigated as an alternative to a conventional spark ignition system. The present study focuses on the extension of the operational limits for lean and diluted combustion using the repetitive nanosecond pulse discharges. First, in order to investigate the flame kernel formation process when the repetitive nanosecond pulse discharges are used, the initial flame kernel is observed using Schlieren photography with a high speed camera. As a result, the flame kernel generated by repetitive pulse discharges is larger than by a conventional ignition system.
Journal Article

Effect of Fuel and Thermal Stratifications on the Operational Range of an HCCI Gasoline Engine Using the Blow-Down Super Charge System

2010-04-12
2010-01-0845
In order to extend the HCCI high load operational limit, the effects of the distributions of temperature and fuel concentration on pressure rise rate (dP/dθ) were investigated through theoretical and experimental methods. The Blow-Down Super Charge (BDSC) and the EGR guide parts are employed simultaneously to enhance thermal stratification inside the cylinder. And also, to control the distribution of fuel concentration, direct fuel injection system was used. As a first step, the effect of spatial temperature distribution on maximum pressure rise rate (dP/dθmax) was investigated. The influence of the EGR guide parts on the temperature distribution was investigated using 3-D numerical simulation. Simulation results showed that the temperature difference between high temperature zone and low temperature zone increased by using EGR guide parts together with the BDSC system.
Technical Paper

A Study of High Compression Ratio SI Engine Equipped with a Variable Piston Crank Mechanism for Knocking Mitigation

2011-08-30
2011-01-1874
To avoid knocking phenomena, a special crank mechanism for gasoline engine that allowed the piston to move rapidly near TDC (Top Dead Center) was developed and experimentally demonstrated in the previous study. As a result, knocking was successfully mitigated and indicated thermal efficiency was improved [1],[2],[3],[4]. However, performance of the proposed system was evaluated at only limited operating conditions. In the present study, to investigate the effect of piston movement near TDC on combustion characteristics and indicated thermal efficiency and to clarify the knock mitigation mechanism of the proposed method, experimental studies were carried out using a single cylinder engine with a compression ratio of 13.7 at various engine speeds and loads. The special crank mechanism, which allows piston to move rapidly near TDC developed in the previous study, was applied to the test engine with some modification of tooling accuracy.
Journal Article

A Study of Newly Developed HCCI Engine With Wide Operating Range Equipped With Blowdown Supercharging System

2011-08-30
2011-01-1766
To extend the operating range of a gasoline HCCI engine, the blowdown supercharging (BDSC) system and the EGR guide were developed and experimentally examined. The concepts of these techniques are to obtain a large amount of dilution gas and to generate a strong in-cylinder thermal stratification without an external supercharger for extending the upper load limit of HCCI operation whilst keeping dP/dθmax and NOx emissions low. Also, to attain stable HCCI operation using the BDSC system with wide operating conditions, the valve actuation strategy in which the amount of dilution gas is smaller at lower load and larger at higher load was proposed. Additionally to achieve multi-cylinder HCCI operation with wide operating range, the secondary air injection system was developed to reduce cylinder-to-cylinder variation in ignition timing. As a result, the acceptable HCCI operation could be achieved with wide operating range, from IMEP of 135 kPa to 580 kPa.
Technical Paper

A Study of Control Strategy for Combution Mode Switching Between HCCI and SI With the Blowdown Supercharging System

2012-04-16
2012-01-1122
To find an ignition and combustion control strategy in a gasoline-fueled HCCI engine equipped with the BlowDown SuperCharging (BDSC) system which is previously proposed by the authors, a one-dimensional HCCI engine cycle simulator capable of predicting the ignition and heat release of HCCI combustion was developed. The ignition and the combustion models based on Livengood-Wu integral and Wiebe function were implemented in the simulator. The predictive accuracy of the developed simulator in the combustion timing, combustion duration and heat release rate was validated by comparing to experimental results. Using the developed simulator, the control strategy for the engine operating mode switching between HCCI and SI combustion was explored with focus attention on transient behaviors of air-fuel ratio, A/F, and gas-fuel ratio, G/F.
Journal Article

Visualization and Analysis of LSPI Mechanism Caused by Oil Droplet, Particle and Deposit in Highly Boosted SI Combustion in Low Speed Range

2015-04-14
2015-01-0761
In this study, in order to clarify the mechanism of preignition occurrence in highly boosted SI engine at low speed and high load operating conditions, directphotography of preignition events and light induced fluorescence imaging of lubricant oil droplets during preignition cycles were applied. An endoscope was attached to the cylinder head of the modified production engine. Preigntion events were captured using high-speed video camera through the endoscope. As a result, several types of preignition sources could be found. Preignition caused by glowing particles and deposit fragments could be observed by directphotography. Luminous flame was observed around the piston crevice area during the exhaust stroke of preignition cycles.
Technical Paper

Numerical Simulation to Understand the Cause and Sequence of LSPI Phenomena and Suggestion of CaO Mechanism in Highly Boosted SI Combustion in Low Speed Range

2015-04-14
2015-01-0755
The authors investigated the reasons of how a preignition occurs in a highly boosted gasoline engine. Based on the authors' experimental results, theoretical investigations on the processes of how a particle of oil or solid comes out into the cylinder and how a preignition occurs from the particle. As a result, many factors, such as the in-cylinder temperature, the pressure, the equivalence ratio and the component of additives in the lubricating oil were found to affect the processes. Especially, CaCO3 included in an oil as an additive may be changed to CaO by heating during the expansion and exhaust strokes. Thereafter, CaO will be converted into CaCO3 again by absorbing CO2 during the intake and compression strokes. As this change is an exothermic reaction, the temperature of CaCO3 particle increases over 1000K of the chemical equilibrium temperature determined by the CO2 partial pressure.
Technical Paper

Numerical Analysis of Combustion and Flow Inside a Small Rotary Engine for Developing an Unmanned Helicopter

2007-10-30
2007-32-0098
For a disaster relief and automatic inspections, an unmanned helicopter is strongly expected. To develop this, a very high power density source is required. A Wankel-type rotary engine can be the best candidate for the power source. In this study, the development of a very small rotary engine with a displacement of 30 cc is targeted. In order to improve the combustion efficiency, gas exchange and stable ignition, a multi dimensional simulation inside the combustion chamber was carried out. At first, the effect of volumetric efficiency on the maximum power is mentioned. Secondly, the effect of scavenging efficiency is discussed. Thirdly, a blow off through a plug hole is described. The position of plug hole was found important to reduce the blow off amount. Finally, the effect of combustion speed on the engine performance is predicted. As a result, the proposed design will be tested using a proto-type engine.
Technical Paper

Measurement of the Local Gas Temperature at Autoignition Conditions Inside the Combustion Chamber Using a Two-Wire Thermocouple

2006-04-03
2006-01-1344
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.
Technical Paper

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

2006-11-13
2006-32-0098
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.
Technical Paper

Development of a Novel Ignition System Using Repetitive Pulse Discharges: Ignition Characteristics of Premixed Hydrocarbon-Air Mixtures

2008-04-14
2008-01-0468
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 CH4 and C3H8-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.
Journal Article

Development of a Novel Ignition System Using Repetitive Pulse Discharges: Application to a SI Engine

2009-04-20
2009-01-0505
A newly developed small-sized IES (inductive energy storage) circuit with semiconductor switch at turn-off action was successfully applied to an ignition system. This IES circuit can generate repetitive nanosecond pulse discharges. An ignition system using repetitive nanosecond pulse discharges was investigated as an alternative to conventional spark ignition systems. Experiments were conducted using spherically expanding flame configuration for CH4 and C3H8-air mixtures under various conditions. The ignition system using repetitive nanosecond pulse discharges was found to improve inflammability of lean combustible mixtures, such as extended flammability limits, shorted ignition delay time, with increasing the number of pulses. The authors seek for the mechanisms for improving the inflammability in more detail to optimize ignition system, and verify the effectiveness of IES circuit in EGR condition, for real engine use.
Technical Paper

An Experimental Study of a Gasoline HCCI Engine Using the Blow-Down Super Charge System

2009-04-20
2009-01-0496
The objective of this study is to extend the high load operation limit of a gasoline HCCI engine. A new system extending the high load HCCI operation limit was proposed, and the performance of the system was experimentally demonstrated. The proposed system consists of two new techniques. The first one is the “Blow-down super charging (BDSC) system”, in which, EGR gas can be super charged into a cylinder during the early stage of compression stroke by using the exhaust blow-down pressure wave from another cylinder phased 360 degrees later/earlier in the firing order. The other one is “EGR guide” for generating a large thermal stratification inside the cylinder to reduce the rate of in-cylinder pressure rise (dP/dθ) at high load HCCI operation. The EGR guides consist of a half-circular part attached on the edge of the exhaust ports and the piston head which has a protuberant surface to control the mixing between hot EGR gas and intake air-fuel mixture.
Technical Paper

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

2005-04-11
2005-01-0240
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.
Technical Paper

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

2004-09-27
2004-32-0080
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.
Technical Paper

Evaluation of a Concept for DI Gasoline Combustion Using Enhanced Gas Motion

1998-02-23
980152
A direct injection gasoline engine system which employs a unique combustion system with enhanced gas motion is evaluated. Enhanced gas motion is produced by employing both a moderately strong swirl flow and a cavity in the piston. Advantages of this system are that the injection timing or spark timing need not be controlled severely and that since the injection timing can be set at near the intake BDC, time for evaporation can be gained to reduce soot emissions. Problems to be improved are that the Nox emissions level is worse than other lean burn systems and full load operation is not evaluated. According to the numerical calculations, the problems may be solved by enhancing the in-cylinder gas motion with axial stratification of swirl intensity at intake BDC; strong swirl near the cylinder head and weak swirl near the piston surface.
Technical Paper

Combustion Characteristics of a Direct Injection Stratified Charge Rotary Engine Using Spark Ignition and Pilot Flame Ignition Systems

2002-10-29
2002-32-1791
A Direct Injection Stratified Charge Rotary Engine (DISC-RE) with a pilot flame ignition system which has high ignition energy, large flame contact area and long duration of ignition source, has been examined comparing with a spark ignition system, using a model combustion chamber simulating a DISC-RE. As a result, it was found that the combustion using the pilot flame ignition system was activated and that a better ignitability was attained under lean mixture conditions than using a spark ignition system. To analyze these experimental results, numerical calculations of the mixture formation and combustion process were carried out. Numerical analyses proved that the pilot flame ignition system was superior to the spark ignition system as the pilot flame ignition made large-area ignition source and large inflammable mixture region. Finally, a single rotor with 650 cc displacement DISC-RE was built as a prototype.
Technical Paper

Improvement in Thermal Efficiency of Lean Burn Pre-Chamber Natural Gas Engine by Optimization of Combustion System

2017-03-28
2017-01-0782
To understand the mechanism of the combustion by torch flame jet in a gas engine with pre-chamber and also to obtain the strategy of improving thermal efficiency by optimizing the structure of pre-chamber including the diameter and number of orifices, the combustion process was investigated by three dimensional numerical simulations and experiments of a single cylinder natural gas engine. As a result, the configuration of orifices was found to affect the combustion performance strongly. With the same orifice diameter of 1.5mm, thermal efficiency with 7 orifices in pre-chamber was higher than that with 4 orifices in pre-chamber, mainly due to the reduction of heat loss by decreasing the impingement of torch flame on the cylinder linear. Better thermal efficiency was achieved in this case because the flame propagated area increases rapidly while the flame jets do not impinge on the cylinder wall intensively.
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