Expansion Stroke Research Articles

A study on the direct control of the start of homogeneous charge compression ignition combustion by pulsed flame jet with rapid compression expansion machine

Aiming at direct ignition-timing control of homogeneous charge compression ignition in low-load conditions, pulsed flame jet, which is the jet of burning gas issuing from a small cavity facing a combustion chamber, was utilized. The characteristics of homogeneous charge compression ignition combustion initiated by pulsed flame jet were investigated using rapid compression expansion machine, which realizes single compression and expansion strokes and thus the measurement of indicated work. Higher indicated mean effective pressure was obtained using pulsed flame jet without increasing NOx emission drastically, and it was shown that pulsed flame jet has potential to control the onset of homogeneous charge compression ignition combustion appropriately. The validity of pulsed flame jet utilization was shown through pressure and NOx measurements.

Direct numerical simulations of HCCI/SACI with ethanol

Two and three dimensional direct numerical simulations (DNS) of an autoignitive premixture of air and ethanol in Homogeneous Charge Compression Ignition (HCCI) mode have been conducted. A special feature of these simulations is the use of compression heating through mass source/sink terms to emulate the compression and expansion due to piston motion. Furthermore, combustion phasing is adjusted such that peak heat release occurs after Top Dead Center (TDC) during the expansion stroke, as in a real engine. Zero dimensional simulations were first conducted to identify important parameters for the higher dimensional simulations. They showed that for ethanol, temperature and dilution are the parameters the problem is most sensitive to. One set of two dimensional simulations were conducted with a uniform mixture composition and different levels of temperature stratification, both with and without compression heating. Another set of simulations varied the mixture stratification with constant temperature stratification. Both sets showed considerable differences in ignition delay, heat release and peak temperature and peak pressure. Compression heating was also found to have a significant effect on the heat release profile. A three dimensional simulation was conducted for Spark-Assisted HCCI (SACI). It was initiated with a small spark kernel, which evolved into a premixed flame. The entire mixture eventually underwent autoignition. Distance function based analysis showed a strongly attenuating flame. Analysis of scalar mixing frequencies shows that differential diffusion and reaction induced mixing play an important role in predicting the mixing of reactive scalars. This has significant implications for mixing models for reactive flows. Chemical explosive mode analysis (CEMA) was applied to the 3D simulation and showed promise in identifying the transition from flame propagation to autoignition.

Thermodynamic Simulation and Prototype Testing of a Four-Stroke Free-Piston Engine

In order to achieve higher-energy conversion efficiency, a free-piston engine with an improved four-stroke thermodynamic cycle is investigated in this paper. This cycle is optimized according to the variable strokes feature and is characterized by the short intake stroke, the complete expansion stroke, the external pressurization, and the intercooling. The development of a four-stroke free-piston engine system simulation model was described, and the effects of the cycle on the system performances were qualitatively analyzed. According to the experiment of the prototype, the generating efficiency of 33.4% can be achieved when the system is fueled with gasoline and the output power is significantly increased from 1.62 to 2.68 kW. The simulation and experiment results are analyzed in detail, giving insight into the performances of the system. Studies show that the energy-saving and environmental protection performances of the system can be significantly promoted by using the improved thermodynamic cycle.

Chickenpox and stroke in children: case studies and literature review

Postvaricella cerebral arteriopathy (PVCA) presents with acute haemiparesis and/or haemidistonia, caused by ischaemic lesions of internal capsule and/or basal ganglia, related to stenosis of proximal middle and/or anterior cerebral arteries. Anti-aggregant drugs are recommended to prevent thrombus expansion and recurrent stroke, but neurologic outcome is usually good regardless of the therapeutic approach. Chickenpox should be considered in differential diagnosis of ischaemic stroke in healthy children who fit the clinical and radiological typical profile of PVCA.

I211 ガソリンの壁面付着に伴うすす生成の数値解析

Liquid fuel films attached on wall surfaces are presumed to cause soot emissions during the cold startup period of gasoline direct injection spark ignition engines. In this study, soot formation originated in combustion of liquid fuel films was investigated by using a 3D simulation. Calculations were performed for a Rapid Compression and Expansion Machine model. Effects of physical properties and the composition of the fuel were examined. Results showed that a portion of liquid fuel films remained until the end of the expansion stroke without evaporating even with the passage of the flame under the cold startup condition. Emission factors of liquid fuel films and soot were lager for PRF095 (i-C_8H_<18> 83%, n-C_7H_<16> 4%, C_6H_5CH_3 13%) than those of PRF100 (i-C_8H_<18> 100%). PRF100-ND having evaporation properties same as n-C_<10>H_<22> and chemical kinetics same as i-C_8H_<18> was prepared numerically. Emission factors of PRF100-ND were larger for liquid fuel films and smaller for soot than other fuels under the cold startup condition.

Analysis on Three Dimensional Flow of Direct-injection Diesel Engine for Different Piston Configuration using CFD

Recent years have witnessed rapid developments in the field of IC engines. Today both the manufacturers and the customers are looking for low polluting and better efficient engines. Basically, the in-cylinder gas motion affects the performance of the engine. Increase in combustion efficiency obviously results in fuel economy and low pollutant emissions. So, it is necessary to have a better control over in-cylinder gas motion. The main objective of this project is three dimensional flow calculations of the compression stroke of a four-valve direct-injection Diesel engine for different Piston configuration. A limited number of validation calculations of the Intake stroke and compression stroke were performed in order to explore the limits of Computational Fluid Dynamics representation of the in-cylinder flow. In the main study, the flow characteristics such as Swirl Ratio, Radial Velocity field and Tangential Velocity field inside the engine cylinder equipped with different piston configurations were analyzed in detail. The results confirmed that the piston geometry had little influence on the in-cylinder flow during the Intake stroke and the first part of Compression stroke. The bowl shape plays a significant role near TDC and in the early stage of the expansion stroke by controlling the turbulence velocity fields.

Motion Characteristics and Influence Factors of Piston Assembly in a Compression-Ignition Hydraulic Free-Piston Engine

The advantages and basic structure of hydraulic free-piston engine (HFPE) were presented. And the operation principle of a single piston compression-ignition HFPE was analyzed. Based on the basic theory of thermodynamics, hydraulic fluid mechanics and dynamics, the system simulation model for a single-piston compression-ignition HFPE was established in the environment of MATLAB/SIMULINK. The simulation results, which accord with the related literature data, indicate that the asymmetric characteristics of piston motion in the entire cycle are very obvious, the compression stroke duration is longer than the expansion stroke, the time at around the top dead center (TDC) is short. The piston assembly motion is a process when the energy balance is fulfilled, and some factors must be taken into account for design optimization, such as the piston assembly mass, compression accumulator pressure, fuel injection timing and fuel injection quantity.

Investigation of anisotropic plastic deformation of advanced high strength steel

Influences of constitutive models on plastic behavior of a TRansformation Induced Plasticity (TRIP) high strength steel were investigated. Different yield criteria, the von Mises's isotropic, Hill's anisotropic (Hill'48) and Barlat's anisotropic (Yld2000-2d) function were taken into account. The hardening laws with regard to Swift and Voce model were examined. To determine material properties for different states of stress and loading directions, uniaxial tensile test, balanced biaxial test and disk compression test were performed. The yield stresses and r-values calculated according to the yield criteria were primarily compared with the experimental results. Afterwards, tensile test of sheet samples with various notch geometries as well as hole expansion test were carried out experimentally and simulated by the finite element method. Distributions of stress and strain within critical area of each notched sample were determined and effects of the yield functions and hardening models on the predicted stress triaxialities and plastic strain localizations were studied. In case of the hole expansion test, punch load and stroke, final hole diameter and strain distribution along the hole circumference and specimen diameter in the rolling and transverse directions were characterized and compared with the calculations. The anisotropic yield potential and hardening behavior significantly affected accuracies of the predicted local deformation behavior of the high strength steel sheet. It was shown that the Yld2000-2d model based on the Swift model with the exponent of six better agreed with the experimental data than other alternatives.

Combustion and soot processes of diesel and rapeseed methyl ester in an optical diesel engine

In-cylinder combustion and soot processes for ultra-low sulphur diesel (ULSD) and rapeseed methyl ester (RME) fuels were investigated in an optically accessible high speed direct injection diesel engine (HSDI) using in situ optical and laser measurement techniques. High speed imaging techniques were used to study the spatial distribution of spray flames, soot formation and oxidation through simultaneous measurements of OH* chemiluminescence and natural soot luminosity, during the luminous combustion process. The amount of un-oxidised soot left in the cylinder after the end of luminous combustion for these fuels were investigated using planar laser induced incandescence (PLII). In addition to PLII, time resolved laser induced incandescence (TR-LII) technique was used simultaneously to explore crank angle resolved variation of primary soot particle size during the expansion stroke. The ignition for RME occurs earlier compared to ULSD, and the early phase of RME combustion proceeds quicker compared to ULSD. The flame lift off length (FLoL) and the length based on the first appearance of soot (SLoL) are longer for RME. The combined effect of relatively longer FLoL and the presence of fuel-bound oxygen reduced the overall soot formation process for RME. PLII data confirmed that the relative amount of soot left in the cylinder after the end of visible luminous combustion is less for RME, and the soot formed are oxidised well within the combustion chamber before it is exhausted out of the engine compared to ULSD. The measured in-cylinder primary soot particles are in the size range between 15 and 35nm and it decreases with crank angle. The sizes of particles generated from the combustion of RME were slightly smaller compared to ULSD.

Power and Efficiency Analysis of Diesel Cycle Under Alternative Criteria

Model studies of the internal combustion engine cycles are useful for illustrating some important parameters affecting engine performance. The Diesel cycle is considered as a special case of an internal combustion engine. In the diesel cycle, combustion is controlled in order to obtain constant pressure at the beginning of the expansion stroke. It is important to choose the proper optimization criterion for the optimum design of the internal combustion engines. The choice of optimization criterion can be changed depending on the purpose of engine design and working conditions of the internal combustion engine. In this study, a comparative performance analysis is carried out for a reversible air standard Diesel cycle based on three alternative performance criteria, namely, maximum power (mp), maximum power density (mpd) and maximum efficient power (mep). The effects of the design parameters such as volume ratio and extreme temperature ratio of the cycle have been investigated under mp, mpd, mep and maximum efficiency conditions. The results show that the design parameters at mep conditions lead to more efficient engines than that at the mp conditions and that the mep criterion may have a significant power advantage compared to mpd criterion.

Optimize combustion of compressed natural gas engine by improving in-cylinder flows

In order to solve the problem of slow flame propagation in a spark-ignition engine fueled with compressed natural gas (CNG), the influence of in-cylinder flows on combustion process was investigated in CA6SE3-21E4N CNG-engine by means of numerical simulation and experiment. The status of in-cylinder flows from intake to expansion stroke was described by computational fluid dynamic tool, which revealed that the in-cylinder flows were one of the main reasons of slow burning rate. Therefore, a special-shaped combustion chamber called Cross was used to improve the in-cylinder flows. The results showed that peak turbulent kinetic energy of Cross was 43.9% higher than that of original combustion chamber called Cylinder during the late compression period at 1450 rpm 100% load. The combustion parameters, brake specific fuel consumption (BSFC) and regulated emissions were obtained by means of experiment. At 1450rpm 25%, 50%, 75% and 100% load conditions, the ignition delay of Cross was longer than that of Cylinder, moreover, the Cross produced averagely 5.75°CA shorter combustion duration. The BSFC of Cross was on an average of 4.3% reduction at 1450 rpm as well as the HC and CO emissions were reduced whereas the NOx emissions were significantly increased.

A tabulated diffusion flame model applied to diesel engine simulations

The tabulated diffusion flamelet model approximated diffusion flame-presumed conditional moment is here adapted to the Reynolds-averaged Navier–Stokes simulation of diesel engines. The first model modification concerns the effects of variable pressure, which are necessary to retrieve the chemical species concentrations during the expansion stroke. They are accounted for following an approach similar to the variable volume tabulated homogeneous chemistry approach. The second model modification concerns the local fresh gases temperature stratification modeling that needs to be included due to the liquid injection and is based on the transport equation for the fresh gases enthalpy conditioned in the air. The resulting model is called engine approximated diffusion flames and is able to account for the auto-ignition of the diffusion flame, the local mixture fraction heterogeneity through a presumed probability density function, complex chemistry effects, variable pressure, and temperature stratification. As a first validation, an ideal homogeneous adiabatic engine is computed and successfully compared with the reference solution of the same case obtained with a kinetic solver. Then, six diesel engine operating points at various loads, engine speeds, and dilutions are simulated and compared with experimental measurements. It is shown that the proposed model correctly reproduces the mean pressure evolution and gives a correct estimation of the CO mass fraction. Furthermore, coupled to the NO relaxation approach model, relatively accurate NO predictions are obtained. Finally, different simplified formulations of engine approximated diffusion flames are evaluated, showing that all model components are necessary to correctly estimate the pressure evolutions and pollutant emissions.

Improvement of DME HCCI engine combustion by direct injection and EGR

To extend the operating range of a homogeneous charge compression ignition (HCCI) engine fuelled with DME, direct injection and exhaust gas recirculation (EGR) were used to investigate their effects on the change of combustion characteristics in this experiment.Single cylinder engine was used with port fuel injector and direct injector. EGR line was connected from exhaust pipe to intake pipe. The experimental result for direct injection was compared with that for port injection. The gross indicated mean effective pressure (IMEPgross), which represented the operation region, for direct injection was higher than that for port injection due to late combustion resulting from lower temperature combustion induced by evaporating latent heat of injected DME in the cylinder. There was optimal direct injection timing for DME HCCI engine because the combustion characteristics were changed from overall lean combustion to locally rich combustion. IMEPgross was increased by EGR. It was because EGR made tardy combustion and increased positive work during expansion stroke. Consequently, direct injection with optimal injection timing and EGR increased the IMEPgross by 22% and 55% compared to port injection case, respectively.

Mathematical modeling of hydrocarbon emissions from oil film for different fuels

Oil film on the inner surface of the cylinder liner is one of the major sources of the vehicle-out HC emissions as fuel vapor is absorbed by the oil film under high pressure and then released after late expansion stroke when the pressure is low. This process is extensively affected by type of the fuel and lubricating oil. In this theoretical study, the effect of different engine parameters on oil film HC emissions for various fuels, such as iso-octane, methanol, ethanol, LPG and methane, is investigated. The results show that fewer HCs are released from the oil film when using gaseous fuels, such as LPG and methane, than when using liquid fuels. The fuels can be ranked according to their effect (from greatest to least) on HC emissions as follows: iso-octane, methanol, ethanol, LPG and methane. The most important parameters affecting the HC absorption/release mechanism are found to be Henry’s coefficient and the diffusion coefficient. As interaction time of oil film-fuel vapor was longer at low engine speeds, the quantities of HC absorbed/desorbed increased. The quantities of HC absorbed/desorbed increased with increasing inlet pressure and compression ratio.

Effect of hydrogen addition to intake air on combustion noise from a diesel engine

This study investigates the characteristics of combustion noise from a diesel engine with hydrogen added to intake air. The engine noise with hydrogen addition of 10 vol% to the intake air was lower than that with diesel fuel alone at late diesel-fuel injection timings. A transient combustion-noise-generation model was introduced to discuss noise characteristics based on energy conversion from combustion impact to noise via structure vibration. The results show that the maximum combustion impact energy had a predominant effect on the maximum engine noise power for each cycle. Therefore, the combustion noise largely contributed to the total engine noise in an early stage of the expansion stroke. The dependences of engine noise on the diesel-fuel injection timing for different hydrogen fractions are discussed considering the characteristics of maximum combustion impact energy for each frequency.

PROPOSAL OF A PISTON ENGINE WITH CLOSE THERMAL CYCLE OF WORKING MEDIUM

Ecological aspects and utilization of biomass as a fuel leads to applying of a closed work cycle in the piston engine. It forces usually to delivering of heat to working medium through a heat exchanger. The heat may get from any type of fuel in an external combustion chamber, which allows on precisely control of combustion process. The paper describes a new conception of the engine operating in two-stroke cycle with working medium being in the close system, the best with the perfect gas as argon or helium. The delivering process of working medium with high temperature from the heat exchanger takes place through the inlet valve during a few dozen degrees of CA rotation in piston position at TDC. Expansion stroke takes place until outlet valve opens shortly BBDC. The outlet period from the cylinder follows almost at constant pressure and at low temperature to an adiabatic chamber, from where the working medium is compressed by an adiabatic compressor to pressure near pressure being in the heat exchanger. The engine works in two-stroke cycle and enables to get low temperature and pressure as early as BDC through a long time of opening of the outlet valve. The paper presents the ideological scheme of the engine system and theoretical thermal cycle. On this basis one presents the theoretical description of the individual thermodynamic processes with determination of thermal parameters of the characteristic points of the cycle. This article determines also the thermal efficiency of such closed cycle. The presented engine may have a practical applying as a stationary engine in energetic systems, where as fuel may be biomass, which globally influences on decreasing of CO2 and NOx by temperature control of the combustion process.

Application of Generalized RNG Turbulence Model to Flow in Motored Single-Cylinder PFI Engine

This paper describes a generalized renormalization group (RNG) turbulence model applied to simulate non-reacting flows in an optical single-cylinder PFI engine. A structured computational mesh of the combustion system with complex geometry was generated by ICEM-CFD in conjunction with KIVA-3V code. Turbulent flow in the 4-valve engine, including the exhaust, intake, compression and expansion strokes, was simulated with the standard k – ε and a generalized RNG turbulence model using the KIVA-3V code. Crank angle-resolved results from available experimental data were used as the boundary and initial conditions for the calculation setup. Pressure traces of the simulation results were compared to the phase-averaged measured pressure trace. Predicted radial and vertical velocities along a horizontal line at BDC and radial velocities along the cylinder axis at four crank angles were compared with the experimental measurements. In addition, the velocity field calculated by the generalized RNG turbulence model was compared with experimental data from Particle Image Velocimetry (PIV) measurements. Good agreement was found between the experiment results and simulation results with the generalized RNG turbulence model.

The atmospheric steam engine as energy converter for low and medium temperature thermal energy

Many industrial processes and renewable energy sources produce thermal energy with temperatures below 100 °C. The cost-effective generation of mechanical energy from this thermal energy still constitutes an engineering problem. The atmospheric steam engine is a very simple machine which employs the steam generated by boiling water at atmospheric pressures. Its main disadvantage is the low theoretical efficiency of 0.064. In this article, first the theory of the atmospheric steam engine is extended to show that operation for temperatures between 60 °C and 100 °C is possible although efficiencies are further reduced. Second, the addition of a forced expansion stroke, where the steam volume is increased using external energy, is shown to lead to significantly increased overall efficiencies ranging from 0.084 for a boiler temperature of T0 = 60 °C to 0.25 for T0 = 100 °C. The simplicity of the machine indicates cost-effectiveness. The theoretical work shows that the atmospheric steam engine still has development potential.

Computational study of crevice soot entrainment in a diesel engine

In this reported work, operating parameters affecting spatial evolution of combustion soot and the associated transport processes into crevice region in a light-duty diesel engine were appraised. Numerical computation of diesel combustion was undertaken by means of linking a plug-in chemistry solver namely, CHEMKIN-CFD into ANSYS FLUENT 12, a commercial Computational Fluid Dynamics (CFD) software. The mesh domain comprised the crevice region to allow quantitative and qualitative inspections of species entrained into the crevice. Effects on the soot spatial evolution and the soot entrainment into crevice and region near the cylinder liner are studied for different injection strategies. This includes single injection with different start of injection (SOI) timings, as well as two main injection pulses with different fuel mass distribution and dwell period in between the two. Soot entrainment process is found to occur through two phases, which is after the ignition process and at the end of the expansion stroke. Most significant soot mass entrainment is found in cases with retarded fuel injection and split-main injection with large separation in between the pulses. Advancing the SOI reduces the soot concentration in the combustion chamber and correspondingly moderates the soot entrainment process. Implementing a close-coupled injection has a more significant effect in reducing soot entrainment in the late injection cases as compared to those with advanced injection. Amount of soot near the cylinder liner for all cases are between 20 and 2000 times higher than those in the crevice region, and soot entrainment via mass transport is dominant as compared to the soot formation near the crevice. For future investigation, improvement can be made to the CFD sub models to account for the thermophoretic effect on soot deposition process.

Post injection in a compression ignition engine fueled with dimethyl-ether

The effects of post injection on engine combustion characteristics and emission reduction were investigated at low speed and low load conditions. Combustion performance and exhaust emissions were tested by varying the post injection timings and quantities. The main injection was fixed at 2 crank angle degree after top dead center. Post injection timing varied from 12 to 50 crank angle degree after top dead center. The fuel quantity of post injection varied from 1 to 3mg, and the fuel quantity from main injection was adjusted to maintain a constant load.The fuel quantity from main injection with post injection was smaller than that of single injection because the fuel injection was split into two. This reduced the pressure rise rate and the heat release rate during main combustion. The effects of post injection on main combustion diminished as post injection timing retarded. Hydrocarbon and carbon monoxide emissions were reduced with post injection close to the main injection. As the post injection timing was retarded, the post combustion temperature was lowered due to volume expansion during the expansion stroke. This increased the hydrocarbon and carbon monoxide emissions for late post injection timing. Despite decreased in-cylinder gas temperature with retarded post injection, hydrocarbon and carbon monoxide emissions declined at 20 crank angle degree post injection, and minimum fuel consumption was noted at 25 crank angle degree post injection. The fuel spray was placed on the top outside corner for post injection at 20 and 25 crank angle degree, and this improved the remaining air usage after main combustion. Oxides of nitrogen emissions were reduced with a post injection. The post combustion reduced the main fuel quantity by the split injection. This reduced oxides of nitrogen production during the main combustion. Post combustion occurred at low in-cylinder gas temperature and released small amount of heat. Therefore, post combustion did not contribute in the production of oxides of nitrogen emissions.