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Journal Article

The Effects of Ignition Environment and Discharge Waveform Characteristics on Spark Channel Formation and Relationship between the Discharge Parameters and the EGR Combustion Limit

2015-09-01
2015-01-1895
In order to realize the high compression ratio and high dilution combustion toward improvement in thermal efficiency, the improvement in stability of ignition and initial phase of combustion under the high gas flow field is the major challenge. In terms of the shift on the higher power side of the operating point by downsizing and improvement of real world fuel consumption, the improvement of ignitability is increasingly expected in the wide operating range also including high load and high engine speed region. In this study, the effects of the gas pressure, gas flow velocity near the spark gap at ignition timing, and discharge current characteristics on spark channel formation were analyzed, focusing on restrike event and spark channel stretching in the spark channel formation process. And the relationship between the average discharge current until 1 ms and the EGR combustion limit was considered.
Technical Paper

Mixture Formation Analysis of a Schnurle-Type Two-Stroke Gasoline DI Engine

2001-03-05
2001-01-1091
Because the two-stroke gasoline engine has a feature of high power density, it might become a choice for automobiles' power train if the high HC exhaust emissions and high fuel consumption rate could be improved. As the GDI technology is quite effective for two-stroke engines, a Schnurle-type small engine was modified to a GDI engine, and its performance was tested. Also, numerical analysis of the mixture-formation process was carried out. Results indicated it was possible to reduce both the HC emissions and fuel consumption drastically with the same maximum power as a carbureted engine at WOT condition. However, misfiring in light load condition was left unresolved. Numerical analysis clarified the process of how the mixture formation got affected by the injector location, injection timing, and gas motion.
Technical Paper

Numerical Analysis of Mixture Preparation in a Reverse Uniflow-Type Two-Stroke Gasoline DI Engine

2001-12-01
2001-01-1815
The authors have been engaged in developing a new-generation two-stroke gasoline engine which could be employed ultimately for automobiles. By investigating the defects of the Schnurle-type two-stroke gasoline engine, a reverse uniflow-type direct injection engine has been developed and built. The newly introduced system employs stratified charge combustion in light to medium load conditions by using the technology already developed for the four-stroke direct injection gasoline engines while it can supply the maximum power output by using a super-charger and attaining homogeneous combustion. Engine performance is being tested experimentally. In order to analyze the performance test results, numerical analysis of in-cylinder phenomena, such as gas-exchange, gas motion, fuel spray formation, and mixture formation is carried out in this paper.
Technical Paper

Research and Development of a Direct Injection Stratified Charge Rotary Engine with a Pilot Flame Ignition System

2001-12-01
2001-01-1844
A Direct Injection Stratified Charge Rotary Engine ( DISC-RE ) with a pilot flame ignition system has been studied to find the possibility of simultaneous reductions of fuel consumption rate and HC exhaust gas emissions. Firstly, combustion characteristics in a model combustion chamber, which simulates the DISC-RE were examined from the viewpoints of calculation and experiment. The high speed photography and the indicated pressure analysis were experimentally performed while numerical calculations of the mixture formation and combustion processes were also carried out. As a result, it has been found that the combustion using the pilot flame ignition system is much activated and a better ignitability is attained under lean mixtures than using a spark ignition system. Secondly, a single rotor with 650 cc displacement DISC-RE was built as a prototype. Combustion characteristics and its performance were tested using a combustion analyzer.
Technical Paper

Effects of Fuel and Diluents on Stratified Charge Turbulent Combustion in Simplified Conditions

2003-05-19
2003-01-1807
Stratified charge combustion system is widely used for production engines due to the significant potentials, such as low fuel consumption rate and low exhaust gas emissions. The combustion phenomena in simplified stratified charge conditions have been examined with changing the initial turbulence intensity, degree of mixture charge stratification, and kinds of fuels in order to clarify the features. Moreover, it should be noted that the stratified charge combustion may cause raising NOx formation. EGR (Exhaust Gas Recirculation) system is widely used for this solution. In this study, EGR was simulated by using dilution gases, such as CO2 and N2. Combustion characteristics in homogeneous and stratified charge fields with dilution gas were examined. As a result, some interesting combustion characteristics between CO2 and N2 depending on the specific heat, initial turbulence intensity, and degree of charge stratification were found.
Technical Paper

Visualization of the Heat Transfer Surface of EGR Cooler to Examine Soot Adhesion and Abruption Phenomena

2017-03-28
2017-01-0127
Among the emerging technologies in order to meet ever stringent emission and fuel consumption regulations, Exhaust Gas Recirculation (EGR) system is becoming one of the prerequisites particularly for diesel engines. Although EGR cooler is considered to be an effective measure for further performance enhancement, exhaust gas soot deposition may cause degradation of the cooling. To address this issue, the authors studied the visualization of the soot deposition and removal phenomena to understand its behavior. Based on thermophoresis theory, which indicates that the effect of thermophoresis depends on the temperature difference between the gas and the wall surface exposed to the gas, a visualization method using a heated glass window was developed. By using glass with the transparent conductive oxide: tin-doped indium oxide, temperature of the heated glass surface is raised.
Technical Paper

Driving Cycle Simulation of a Vehicle with Gasoline Homogeneous Charge Compression Ignition Engine Using a Low-RON Fuel

2016-10-17
2016-01-2297
An improvement of thermal efficiency of internal combustion engines is strongly required. Meanwhile, from the viewpoint of refinery, CO2 emissions and gasoline price decrease when lower octane gasoline can be used for vehicles. If lower octane gasoline is used for current vehicles, fuel consumption rate would increase due to abnormal combustion. However, if a Homogeneous Charge Compression Ignition (HCCI) engine were to be used, the effect of octane number on engine performance would be relatively small and it has been revealed that the thermal efficiency is almost unchanged. In this study, the engine performance estimation of HCCI combustion using lower octane gasoline as a vision of the future engine was achieved. To quantitatively investigate the fuel consumption performance of a gasoline HCCI engine using lower octane fuel, the estimation of fuel consumption under different driving test cycles with different transmissions is carried out using 1D engine simulation code.
Technical Paper

Analyses of Cycle-to-Cycle Variation of Combustion and In-Cylinder Flow in a Port Injection Gasoline Engine Using PIV and PLIF Techniques

2017-10-08
2017-01-2213
Reduction in the cycle-to-cycle variation (CCV) of combustion in internal combustion engines is required to reduce fuel consumption, exhaust emissions, and improve drivability. CCV increases at low load operations and lean/dilute burn conditions. Specifically, the factors that cause CCV of combustion are the cyclic variations of in-cylinder flow, in-cylinder distributions of fuel concentration, temperature and residual gas, and ignition energy. However, it is difficult to measure and analyze these factors in a production engine. This study used an optically accessible single-cylinder engine in which combustion and optical measurements were performed for 45 consecutive cycles. CCVs of the combustion and in-cylinder phenomena were investigated for the same cycle. Using this optically accessible engine, the volume inside the combustion chamber, including the pent-roof region can be observed through a quartz cylinder.
Technical Paper

Numerical Investigation of the Effect of Engine Speed and Delivery Ratio on the High-Speed Knock in a Small Two-Stroke SI Engine

2022-01-09
2022-32-0080
Knocking occurs within the high-speed range of small two-stroke engines used in handheld work equipment. High-speed knock may be affected by the engine speed and delivery ratio. However, evaluation of these factors independently using experimental methods is difficult. Therefore, in this study, these factors were independently evaluated using numerical calculations. The purpose of this study was to clarify the mechanism by which the intensity of high-speed knocking that occurs in small two-stroke engines becomes stronger. The results suggest that temperature inhomogeneity due to insufficient mixing of fresh air and previously burned gas may induce high-speed knocking in the operating range at high engine speeds.
Technical Paper

A Study on Combustion Characteristics of DISC Rotary Engine Using a Model Combustion Chamber

1994-03-01
941028
A model combustion chamber of Wankel type rotary engine was employed to study the DISC RE system. A two-stroke Diesel engine's cylinder head was replaced with this combustion chamber to simulate temporal change of air flow and pressure fields inside the chamber as an actual engine. The base engine was motorized to operate as a continuous rapid compression and expansion machine. Pilot fuel spray was injected onto a glow plug to form a pilot flame and it ignites the main fuel spray. The ignitability of pilot fuel, mixture formation process, ignition process of main fuel by pilot flame and the effect of pilot and main injection timings on combustion characteristics were examined.
Technical Paper

Analysis of DISC Combustion Using a Pilot Flame Ignition System

1994-10-01
941927
A new DISC combustion system with a pilot flame for ignition was analyzed by using a model combustion chamber of a Wankel type rotary engine. A two-stroke diesel engine's cylinder head was replaced with this combustion chamber to simulate temporal changes of air flow and pressure fields inside the chamber as in actual engines. Two types of fuel injection systems were tested to obtain combustion characteristics such as the heat release rate. Direct photographs of spray and combustion were analyzed to understand the mixture-formation process of the main spray and to see the flame temperature distribution and flame moving velocity vectors. In order to understand the mixture-formation process, numerical calculations were made using a gaseous fuel. Finally, the effect of the fuel characteristics on combustion was examined using diesel fuel and n- hexane.
Technical Paper

Analysis of DISC Rotary Engine Combustion Using Improved Pilot Flame Ignition System

1996-10-01
962021
In order to enhance the reliability of a pilot flame ignition system, three kinds of subchambers in which a pilot injector and a glow plug were set up were tested with a model combustion chamber of DISC rotary engine. A two-stroke Diesel engine's cylinder head was replaced with this model combustion chamber to simulate temporal changes of air flow and pressure fields inside the chamber as an actual engine. The behavior of the pilot flame generated in the subchamber, ignition process of main fuel spray by the pilot flame, the most suitable mixture distribution between the main chamber and the subchamber, and the effect of nozzle diameter of main injector on combustion characteristics were studied by using a high-speed video camera and ion probes.
Technical Paper

Performance Tests of Reverse Uniflow-Type Two-Stroke Gasoline DI Engine

2004-09-27
2004-32-0040
Conventional two-stroke engines have defects such as unstable combustion, high fuel consumption rate and high HC emissions. In order to overcome the defects, a direct fuel injection system and a novel scavenging system were adopted. The authors tested a newly developed reverse uniflow-type two-stroke direct injection gasoline engine that was designed by numerical simulations. In comparison with the base engine at low engine speed, HC emission was decreased by up to 80%, and BSFC was reduced by around 40%. Power and BSFC were superior to those of a latest port-injection four-stroke engine. Furthermore, it was found that engine performance of exhaust gas emissions, fuel economy or output power can be selectively optimized by switching homogeneous and stratified combustion.
Technical Paper

Numerical Analysis of Gas Exchange Process in a Small Two-Stroke Gasoline Engine

1999-09-28
1999-01-3330
To survive the severe regulations for both the exhaust gas emissions and fuel economy, research on small two-stroke gasoline engines from both the experimental and theoretical viewpoints is quite necessary. In the present study, firstly, performance tests of a direct injection small two-stroke gasoline model engine were carried out. Based on these experimental results, three-dimensional flow calculations from scavenging pipe to exhaust pipe during the gas-exchange and piston compression processes were made with the same experimental conditions. As a result, the gas exchange process was investigated and some problems were clarified. Secondly, parametric calculations with changing just exhaust port timings were performed to solve the problems found in the above calculations.
Technical Paper

Analysis of Mixture Formation Process in a Reverse Uniflow-Type Two-Stroke Gasoline DI Engine

2002-10-29
2002-32-1774
A reverse uniflow-type two-stroke gasoline direct injection engine, which has potentials of high power weight ratio, high thermal efficiency and low exhaust gas emissions, has been developed and tested. In this study, one of the features of this engine: very low cycle-to-cycle combustion variation at idling condition, is focused to clarify the reasons. To achieve this, a transparent cylinder model engine was designed and built to visualize the in-cylinder mixture formation process, and the free spray characteristics of a swirl-type injector were examined using a large chamber with changing the injection pressure, environmental gas pressure, and the gas temperature. As a result, the reasons of stable idling operation were deduced.
Technical Paper

A Study of the Mechanism of High-Speed Knocking in a Two-Stroke SI Engine with High Compression Ratio

2023-10-24
2023-01-1824
Experimental methods and numerical analysis were used to investigate the mechanism of high-speed knocking that occurs in small two-stroke engines. The multi-ion probe method was used in the experiments to visualize flame propagation in the cylinder. The flame was detected by 14 ion probes grounded in the end gas region. A histogram was made of the order in which flames were detected. The characteristics of combustion in the cylinder were clarified by comparing warming up and after warming up and by extracting the features of the cycle in which knocking occurred. As a result, regions of fast flame propagation and regions prone to auto-ignition were identified. In the numerical analysis, flow and residual gas distribution in the cylinder, flame propagation and self-ignition were visualized by 3D CFD using 1D CFD calculation results as boundary conditions and initial conditions.
Technical Paper

Effect of Coolant Water and Intake Air Temperatures on Thermal Efficiency of Gasoline Engines

2017-11-05
2017-32-0116
An optimization of thermal management system in a gasoline engine is considered to improve thermal efficiency by minimizing the cost increase without largely changing the configuration of engine system. In this study, the influence of water temperature and intake air temperature on thermal efficiency were investigated using an inline four-cylinder 1.2L gasoline engine. In addition, one-dimensional engine simulations were conducted by using a software of GT-SUITE. Brake thermal efficiency for different engine speeds and loads could be quantitatively predicted with changing the cooling water temperature in the cylinder head. Then, in order to predict the improvement of the fuel consumption in actual use, vehicle mode running simulation and general-purpose engine transient mode simulation were carried out by GT-SUITE. As a result, it was found that by controlling the temperatures of the cooling water and intake gas, thermal efficiency can be improved by several percent.
Technical Paper

Performance Investigation of a PFI Gasoline Engine by Applying Various Kinds of Fuel Injectors

2020-01-24
2019-32-0546
In this report, the effect of injection specification, such as droplet size, lengths of nozzle tip and spray angle, on the engine performance was investigated using a 1.2 L port fuel injection (PFI) four-cylinder gasoline engine. The experimental conditions were selected to cover the daily operating mode, including the cold start and catalyst heating process. The experiments were conducted by varying not only the injectors but also the injection timing which was shifted from the exhaust to intake stroke. The results were evaluated by the fuel consumption and exhaust gas emissions. When these tests were conducted on a production engine, a carefully designed tumble generator was installed at the intake port to enhance the intake air flow. As a result, the injection specifications showed a potential to obtain less fuel consumption and lower engine-out emissions was evaluated.
Technical Paper

Numerical Investigation of Knocking in a Small Two-Stroke Engine with a High Compression Ration to Improve Thermal Efficiency

2023-09-29
2023-32-0079
This study aimed to achieve both a high compression ratio and low knock intensity in a two-stroke engine. Previous research has suggested that knock intensity can be reduced by combining combustion chamber geometry and scavenging passaging design for the same engine specifications with a compression ratio of 13.7. In this report, we investigate whether low knock intensity can be achieved at compression ratios of 14.4 and 16.8 by adjusting the combustion chamber geometry and scavenging passage design. As a result, the mechanism by which combustion chamber geometry and scavenging passage design change knock intensity was clarified.
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