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Technical Paper

A Study for Generating Power on Operating Parameters of Powerpack Utilizing Linear Engine

The research shows the experimental results for a free piston linear engine according to operation conditions of the linear engine and the structure of linear generator for generating electric power. The powerpack used in this paper consists of the two-stroke free piston linear engine, linear generators and air compressors. Each parameter of fuel input heat, equivalence ratio, spark timing delay, electrical resistance and air gap length were set up to identify the combustion characteristics and to examine the performance of linear engine. The linear engine was fueled with propane. In the course of all linear engine operations, intake air was inputted under the wide open throttle state. Air and fuel mass flow rate were varied by using mass flow controller and these were premixed by pre-mixing device. Subsequently, pre-mixture was directly supplied into each cylinder.
Technical Paper

Simulation Study of SI-HCCI Transition in a Two-Stroke Free Piston Engine Fuelled with Propane

A simulation study was conducted to examine the transition from SI combustion to HCCI combustion in a two-stroke free piston engine fuelled with propane. Operation of the free piston engine was simulated based on the combination of three mathematical models including a dynamic model, a linear alternator model and a thermodynamic model. The dynamic model included an analysis of the piston motion, based on Newton's second law. The linear alternator model included an analysis of electromagnetic force, which was considered to be a resistance force for the piston motion. The thermodynamic model was used to analysis thermodynamic processes in the engine cycle, including scavenging, compression, combustion, and expansion processes. Therein, the scavenging process was assumed to be a perfect process. These mathematical models were combined and solved by a program written in Fortran.
Technical Paper

An Investigation of the Potential of EGR stratification for Reducing Pressure Rise Rate in HCCI Combustion by using Rapid Compression Machine

HCCI (Homogeneous Charge Compression Ignition) engine is able to achieve low NOx and particulate emissions as well as high efficiency. However, its operation range is limited by the knocking at high load, which is the consequence of excessively rapid pressure rises. It has been suggested that making thermal or fuel inhomogeneities can be used to solve this problem, since these inhomogeneities have proved to create different auto-ignition timing zones. It has also been suggested that EGR (Exhaust Gas Recirculation) has a potential to reduce pressure rise rate. But according to a past report, it was concluded that under the same fueling ratio and CA50 with different initial temperature and EGR ratio, the maximum PRR is almost constant. The purpose of this study is to investigate the fundamental effects of EGR. First, I considered EGR homogeneous charge case. In this case, the effects of EGR and its components like CO₂, H₂O or N₂ on HCCI combustion process is argued.
Journal Article

Closed-Loop Combustion Control of a HCCI Engine with Re-Breathing EGR System

This study experimentally investigates the control system and the algorithm after constructing a HCCI combustion control system for the development of a small HCCI engine fuelled with Dimethyl Ether (DME). This system can control four throttles for the mixing ratio of three gases of in-cylinder (stoichiometric pre-mixture, hot EGR gas and cold EGR gas). At first, the combustion behavior for combustion phasing retarded operation with cold and hot EGR was examined. Then, the potential of model-based and feed back control for HCCI combustion with change of the demand of IMEP was investigated. In the end, the limit of combustion-phasing retard for IMEP and PRR was explored. Results shows that to get high IMEP with acceptable PRR and low coefficient of variation of IMEP, crank angle of 50% heat release (CA50) should be controlled at constant phasing in the expansion stroke. CA50 can be controlled by changing the ratio of pre-mixture, hot EGR gas and cold EGR gas with throttles.
Technical Paper

A Study of Fuel and EGR Stratification to Reduce Pressure-Rise Rates in a HCCI Engine

Problem of HCCI combustion is knocking due to a steep heat release by the ignition that is occurred in each local area at the same time. It is considered that dispersion of auto-ignition timing at each local area in the combustion chamber is necessary to prevent this problem. One of technique of this solution is to make thermal stratification. It could be made by using two-stage ignition fuel, which has large heat release at low temperature reaction. Dispersion of fuel concentration leads to difference of temperature histories while combustion phasing is dispersed at each local area. Also, EGR gas stratification could make difference of temperature histories at each local area because of that of the characteristics. This study examines the effect of mixing stratification by stratifying the charge of fuel and CO2. A single-cylinder engine equipped with optical access was used in experiments, and numerical analysis was executed.
Technical Paper

Potential of Stratification Charge for Reducing Pressure-Rise Rate in HCCI Engines Based on Multi-Zone Modeling and Experiments by using RCM

The charge stratification has been thought as one of the ways to reduce the sharp pressure rises of HCCI combustion. The objective of this study is to evaluate the potential of equivalence ratio, initial temperature, and EGR gas stratifications for reducing pressure-rise rate of HCCI combustion. Using rapid compression machine, the stratified pre-mixture is charged, and compressed to analyze the change of in-cylinder gas pressure and temperature traces during compression process. Based on the experiment results, numerical calculations by CHEMKIN are conducted to more specifically analyze the potential of equivalence ratio, initial temperature, and EGR gas stratifications on the reduction of pressure rise rate. Multi-zone model is used to simulate the thermal stratification, fuel stratification and EGR gas stratification of in-cylinder charge as like real engine.
Technical Paper

An Investigation of the Effects of Fuel Inhomogeneity on the Pressure Rise Rate in HCCI engine using Chemiluminescence Imaging

Theoretically, homogeneous charge compression engines (HCCI) are able to grant a high thermal efficiency, as well as a low NOx and particulate emissions. This ability is mainly due to the combustion process, which, contrary to both Diesel and Gasoline engine, is homogeneous in time and space within the combustion chamber. But despite these advantages, the engine operating condition is limited by the narrow boundaries of misfire at low load and knocking at high load. For that matter, one of the numerous ways of overcoming knocking is to deliberately create fuel inhomogeneities within the combustion chamber, since it has proved to lengthen combustion duration and to drastically reduce maximum pressure rise rate (PRR). Nevertheless, though the global effects of fuel inhomogeneities on PRR have been studied, we lack information that explains this phenomenon.
Journal Article

A Potentiality of Dedicated EGR in SI Engines Fueled by Natural Gas for Improving Thermal Efficiency and Reducing NOx Emission

Recently, a potentiality of Dedicated EGR (D-EGR) concept SI engine has been studied. This concept engine had four cylinders and operated with exhaust gas supplied from the single cylinder to the intake manifold. Compared with conventional SI engines, it was able to increase thermal efficiency and decrease CO, HC, and NOx emission by the high D-EGR ratio 0.25. In this study, numerical analysis of a SI engine with D-EGR system with various D-EGR ratios was conducted for detailed understanding the potentiality of this concept in terms of thermal efficiency and NOx emission. #1 cylinder of assumed engine was used as D-EGR cylinder that equivalence ratio varied from 0.6 to 3.4. Entire exhaust gas from #1 cylinder was recirculated to the other cylinders. The other cylinders run with this exhaust gas and new premixed air and fuel with various equivalence ratios from 0.6-1.0.
Technical Paper

An Investigation on the Auto-Ignition of Fuel-Air Mixture Induced by Release of Oil-Fuel Droplets from Cylinder-Liner Using Multi-Zone Model

This study investigated effects of gas inhomogeneity induced by droplets of fuels and oils on the auto ignition timing and temperature in the direct-injection spark ignition (DISI) engine by means of detailed numerical calculation using multi zone model. Recent researchers pointed out that droplets are made of fuels and oils which mix on the cylinder liner and released from the cylinder liner [1]. During the compression stroke released droplets reach the auto ignition temperature before flame propagation induced by spark ignition. It is called Pre-ignition. In combustion chamber, there is inhomogeneity caused by temperature and mixture distribution. In this study, the effects of gas inhomogeneity produced by droplet on the auto ignition timing and temperature have been investigated using Multi-Zone model of CHEMKIN-PRO by changing initial temperature and initial equivalence ratio. Especially, the volume of first ignition zone is focused on.
Technical Paper

Model-Based Combustion Control of a HCCI Engine using External EGR and the Exhaust Rebreathed

To approach realization of Homogeneous Charge Compression Ignition (HCCI) combustion without external combustion ignition trigger, it is necessary to construct HCCI engine control system. In this study, HCCI research engine equipped with the EGR passage for external EGR and the two-stage exhaust cam for exhaust rebreathed. This system can control the mixing ratio of four gases (air, fuel, rebreathed EGR gas, external EGR gas) of in-cylinder by operating four throttles and fuel injection duration while maintaining acceptable pressure rise rate (PRR) and cycle-to-cycle variation of Indicated Mean Effective Pressure (IMEP), closed-loop control system designed by applying feedback variables (equivalence ratio, combustion-phasing, IMEP) for feedback control. Those control inputs (four throttles and fuel injection) has correlation mutually, control inputs cause interference, response become low and hunching occurs.
Technical Paper

A Study on Supercharged HCCI Natural Gas Engines

The possibility of turbocharging into a natural gas homogeneous charge compression ignition (HCCI) engine is investigated experimentally and by simulation. Experiments are performed using a four-cylinder naturally aspirated engine fitted with an external supercharger and a butterfly valve for back pressure control to simulate a turbocharger with efficiency of 0.64. Based on the test results, the performance and emission characteristics are studied in detail through numerical one-dimensional cycle simulations. The results indicate that the thermal efficiency can be improved by raising the engine compression ratio and lowering the turbocharging pressure. At an engine compression ratio of 21 and turbocharging pressure of 1.9 bar, the brake thermal efficiency reaches 0.43, with NOx emissions of only 10 ppm or less.
Technical Paper

An Investigation of Combustion Control Using EGR for Small and Light HCCI Engine Fuelled with DME

The HCCI engine could offer low NOx, PM emissions and high efficiency. However the operation region of the HCCI combustion is limited because of the knocking at high load and the misfire at low load. Moreover the HCCI principle lacks direct combustion control and needs a system to control the combustion phasing with high accuracy. Today there exists various ways to control the HCCI combustion, such as Variable Valve Train, Variable Compression Ratio, Inlet Air Heating and Dual Fuels. However such variable mechanisms and Inlet Air Heating tend to be heavy and complex. Dual Fuels method needs two types of fuels and has a challenge in infrastructure. In this study, in order to develop a small and light HCCI engine, a simple HCCI combustion control system is proposed. DME (Di-methyl Ether) is used as the fuel to keep the structure small and light. In this system, the mixing ratio of three gases: stoichiometric pre-mixture, hot EGR gas and cold EGR gas is changed by only throttles.
Technical Paper

An Investigation of the Effect of Thermal Stratification on HCCI Combustion by using Rapid Compression Machine

A significant drawback to HCCI engines is the knocking caused by rapid increases in pressure. Such knocking limits the capacity for high-load operation. To solve this problem, thermal stratification in the combustion chamber has been suggested as possible solution. Thermal stratification has the potential to reduce the maximum value of the rate of pressure increase combustion by affecting the local combustion start time and extending the duration of combustion. The purpose of this study was to experimentally obtain fundamental knowledge about the effect of thermal stratification on the HCCI combustion process. Experiments were conducted in a rapid compression machine (RCM) equipped with a quartz window to provide optical access to the combustion chamber. The machine was fueled with DME, n-Butane, n-Heptane and iso-Octane, all of which are currently being investigated as alternative fuels and have different low temperature characteristics.
Technical Paper

Study on Auto-Ignition and Combustion Mechanism of HCCI Engine

In the HCCI (Homogeneous Charge Compression Ignition) engine, a mixture of fuel and air is supplied to the cylinder and auto-ignition occurs resulting from compression. This method can expand the lean flammability limit, realizing smokeless combustion and also having the potential for realizing low NOx and high efficiency. The optimal ignition timing is necessary in order to keep high thermal efficiency. The Ignition in the HCCI engine largely depends on the chemical reaction between the fuel and the oxidizer. Physical methods in conventional engines cannot control it, so a chemical method is demanded. Combustion duration is maintained properly to avoid knocking. In addition, the amount of HC and CO emissions must be reduced. The objective of this study is to clarify the following through calculations with detailed chemical reactions and through experiment with the 2-stroke HCCI engine: the chemical reaction mechanism, and HC and CO emission mechanisms.
Technical Paper

Analysis of the Effect of Charge Inhomogeneity on HCCI Combustion by Chemiluminescence Measurement

In the HCCI Engine, inhomogeneity in fuel distribution and temperature in the pre-mixture exists microscopically, and has the possibility of affecting the ignition and combustion process. In this study, the effect of charge inhomogeneity in fuel distribution on the HCCI combustion process was investigated. Two-dimensional images of the chemiluminescence were captured by using a framing camera with an optically accessible engine in order to understand the spatial distribution of the combustion. DME was used as a test fuel. By changing a device for mixing air and fuel in the intake manifold, inhomogeneity in fuel distribution in the pre-mixture was varied. The result shows that luminescence is observed in a very short time in a large part of the combustion chamber under the homogeneous condition, while luminescence appears locally with considerable time differences under the inhomogeneous condition.
Technical Paper

Combustion Analysis of Natural Gas in a Four Stroke HCCI Engine Using Experiment and Elementary Reactions Calculation

Homogeneous charge compression ignition (HCCI) is regarded as the next generation combustion regime in terms of high thermal efficiency and low emissions. It is difficult to control autoignition and combustion because they are controlled primarily by the chemical kinetics of air/fuel mixture. In this study, it was investigated the characteristics of autoignition and combustion of natural gas in a four-stroke HCCI engine using experiment and elementary reactions calculation. The influence of equivalence ratio, intake temperature, intake pressure and engine speed on autoignition timing, autoignition temperature, combustion duration and the emissions of THC, CO, CO2 were investigated. And also, to clarify the influence of n-butane on autoignition and combustion of natural gas, it was changed the blend ratio of n-butane from 0 mol% to 10 mol% in methane / n-butane / air mixtures.
Technical Paper

17 Study on Auto-Ignition and Combustion Completion of n-Butane in a Two-stroke Homogeneous Charge Compression Ignition (HCCI) Engine

Homogeneous Charge Compression Ignition (HCCI) is good method to be higher efficiency and to reduce NOx emission and particular matter together than conventional SI combustion engine. But HCCI depends on chemical reaction of fuel and air mixture. So controlling of ignition timing is difficult, and HCCI is high THC and CO emissions because temperature can't reach the enough temperature to reduce those. In this study, we investigated factor for auto ignition timing and combustion completion on n-Butane/Air mixture by a two-stroke HCCI engine. Auto Ignition temperature are known to be decided by fuel(1), for n-Butane, the temperature was 1150±30K. And as we researched combustion completion from In-cylinder gas temperature, increasing In-cylinder gas temperature caused high combustion efficiency and low THC, CO emissions.
Technical Paper

Numerical Simulation of Auto-Ignition and Combustion of n-Butane and Air Mixtures in a 4 Stroke HCCI Engine by Using Elementary Reactions

HCCI (Homogeneous Charge Compression Ignition) engine is expected to a new engine to be high efficiency and low emission. But it is difficult to control ignition timing and combustion duration, because ignition and combustion mainly depend on oxidation process of fuel. In this study, the focus is to clear the combustion mechanism of auto-ignition engine. By calculating chemical kinetics of elementary reactions, effects of compression speed, equivalence ratio, initial temperature and compression ratio on auto-ignition were investigated. And also, behaviors of chemical species under auto-ignition process were cleared.
Technical Paper

Measurement of Instantaneous Heat Flux Flowing Into Metallic and Ceramic Combustion Chamber Walls

Accurate measurements of combustion gas temperature and the coefficient of heat transfer between the gas and the combustion chamber wall of internal combustion engine in cyclic operations are difficult at present. Hence the only method available for determination of states of thermal load and heat loss to the combustion chamber wall in a cycle is to measure the instantaneous temperature on the combustion chamber wall surface accurately and precisely using proper thin-film thermocouples, then to calculate the instantanenous heat flux flowing into the wall surface by means of numerical analysis. However, it is necessary to pay adequate attention to the effects of thermophysical properties of the thermocouple materials on the measured values, since any thermocouple consists of several kinds of materials which are different from those of portions to be measured.
Technical Paper

Two–Dimensional Imaging of Formaldehyde Formed During the Ignition Process of a Diesel Fuel Spray

The time of, and location where ignition first occurs in a diesel fuel spray were investigated in a rapid compression machine (RCM) using the two–dimensional techniques of silicone oil particle scattering imaging (SSI), and the planar laser induced fluorescence (LIF) of formaldehyde. Formaldehyde has been hypothesized to be one of the stable intermediate species marking the start of oxidation reactions in a transient spray under compression ignition conditions. In this study, the LIF images of the formaldehyde formed in a diesel fuel spray during ignition process have been successfully obtained for the first time by exciting formaldehyde with the 3rd harmonic of the Nd:YAG laser. SSI images of the vaporizing spray, and the LIF images of formaldehyde were obtained together with the corresponding time record of combustion chamber pressures at initial ambient temperatures ranging from 580 K to 790 K.