Analysis of local convective heat transfer in a spark ignition engine

A computational fluid dynamics (CFD) code is applied to simulate fluid flow, heat transfer and combustion in a four-stroke single cylinder engine with pent roof combustion chamber geometry, having two inlet valves and two exhaust valves. Heat flux and heat transfer coefficient on the cylinder head, cylinder wall, piston, intake and exhaust valves are determined with respect to crank angle position. Results for a certain condition are compared for total heat transfer coefficient of the cylinder engine with available correlation proposed by experimental measurement in the literature and close agreement are observed. It was found that the local value of heat transfer coefficient varies considerably in different parts of the cylinder, but they have equivalent trend with crank angle. Based on the results, new correlations are suggested to predict maximum and minimum convective heat transfer coefficient in the combustion chamber of a SI engine.     

A combined experimental and numerical study of thermal processes, performance and nitric oxide emissions in a hydrogen-fueled spark-ignition engine

This work concerns the study of a spark-ignition engine fueled with hydrogen, using both measured and numerical data at various conditions, focusing on the combustion efficiency, the heat transfer phenomena and heat loss to the cylinder walls, the performance, as well as the nitric oxide (NO) emissions formed, when the fuel/air and compression ratio are varied. For the investigation of the heat transfer mechanism, the local wall temperatures and heat flux rates were measured at three locations of the cylinder liner in a CFR engine. These fluxes can provide a reliable estimation of the total heat loss through the cylinder walls and of the hydrogen flame arrival at specific locations. Together with the experimental analysis, the numerical results obtained from a validated in-house CFD code were utilized for gaining a more complete view of the heat transfer mechanism and the hydrogen combustion efficiency for the various cases examined. The performance of the CFR engine is then identified, since the calculated cylinder pressures are compared with the measured ones, from which performance and heat release rates are calculated and discussed. Further, NO emission studies have been accomplished, with the calculated results not only being compared with the measured exhaust NO ones, but also further processed for conducting an in-depth investigation of the dependence of NO production on the spatial distribution of in-cylinder gas temperature. It is revealed that for lower fuel/air ratio the burned gas temperature is held at low level and the heat loss ratio is quite low. As the load increases and stoichiometric mixtures are used, the wall and in-cylinder gas temperatures increase substantially, together with the heat loss and the NO emissions, owing to the high hydrogen combustion velocity and the consequent high rate of temperature rise. The combustion efficiency is slightly increased, but the indicated efficiency is decreased due to higher heat loss.     

Local heat flux measurements in a hydrogen and methane spark ignition engine with a thermopile sensor

This paper describes an experimental investigation of heat transfer inside a CFR spark ignition engine operated at a constant engine speed of 600 rpm. The heat flux is directly measured under motored and fired conditions with a commercially available thermopile sensor. The heat transfer during hydrogen and methane combustion is compared examining the effects of the compression ratio, ignition timing and mixture richness. Less cyclic and spatial variation in the heat flux traces are observed when burning hydrogen, which can be correlated to the faster burn rate. The peak heat flux increases with the compression ratio, but the total cycle heat loss can decrease due to less heat transfer at the end of the expansion stroke. An advanced spark timing and increased mixture richness cause an increased and advanced peak in the heat flux trace. Hydrogen combustion gives a heat flux peak which is three times as high as the one of methane for the same engine power output.     

Simulation of a porous medium (PM) engine using a two-zone combustion model

Porous medium (PM) engine was a new type engine based on the technique of combustion in porous medium, which can realize homogeneous and stable combustion. In this paper, the combustion and working processes of a specific PM engine were simulated by a two-zone model considering the influences of the mass distribution, heat transfer from the cylinder wall, mass exchange between zones and the heat transfer in porous medium. Influences of operating parameters, e.g. intake temperature and pressure, compression ratio, the excess air ratio on the performance of the PM engine were discussed. It was found out that the porous medium, acting as a heat recuperator, can significantly enhance the evaporation of liquid fuel and preheat the mixture, which promotes the ignition and combustion in the cylinder; and that the initial PM temperature and the compression ratio are critical factors controlling the compression ignition of the mixture.     

气道和燃烧室形状对汽油机缸内流场影响的计算研究

为探究气道及燃烧室形状对汽油机缸内流场的影响,以某1.4L多点进气道喷射(MPI)汽油机为研究对象,利用AVL-FIRE软件对原机进气道形状进行稳态数值模拟计算,并对原汽油机在2 800r/min最低比油耗工况点进气及燃烧过程进行瞬态数值模拟计算。基于计算结果对进气道及燃烧室形状进行优化设计,提出4种计算方案,对优化前后各计算方案的缸内速度场、湍动能场、火焰前锋面密度和瞬时放热率进行对比分析。结果显示:改进气道的滚流比明显高于原机气道;结合改进气道,进气侧凸起活塞能够更好地维持滚流;在点火时刻,改进气道结合进气侧凸起活塞这一计算方案的缸内湍流分布及湍动能优于改进气道结合大曲率凹坑活塞、原机气道结合原机活塞(压缩比12)与原机计算方案,点火后火焰传播速度最大,燃烧速度最快。优化进气道及燃烧室形状能够加强缸内气流运动,提高点火时刻缸内湍流强度,加速火焰传播,改善燃烧过程。     

各种因素对柴油机气缸内气体和壁面传热影响的研究

在一台单缸柴油机上，采用表面热电偶测量气缸盖壁面的温度波动，应用一维非稳态传热模型计算了气缸盖壁面不同位置的瞬态传热率。在此基础上，分析了转速、负荷、冷却水温、进气温度、压缩比、壁面不同位置等对壁面温度波动和瞬时传热率的影响，得出柴油机气缸内燃气和壁面间的瞬态传热与壁面温度波动水平有关，气缸内气流速度对气缸内传热有较大的影响等结论。     

Natural gas HCCI engine operation with exhaust gas fuel reforming

Natural gas has a high auto-ignition temperature, requiring high compression ratios and/or intake charge heating to achieve homogenous charge compression ignition (HCCI) engine operation. It is shown here that hydrogen in the form of reformed gas helps in lowering the intake temperature required for stable HCCI operation. It has been shown that the addition of hydrogen advances the start of combustion in the cylinder. This is a result of the lowering of the minimum intake temperature required for auto-ignition to occur during the compression stroke, resulting in advanced combustion for the same intake temperatures. This paper documents experimental results using closed loop exhaust gas fuel reforming for production of hydrogen. When this reformed gas is introduced into the engine, a decrease in intake air temperature requirement is observed for a range of engine loads. Thus for a given intake temperature, lower engine loads can be achieved. This would translate to an extension of the HCCI lower load boundary for a given intake temperature.     

陶瓷隔热发动机缸内传热研究

本运用１维边界层传热模型研究了燃烧室壁面温度变化引起边界层厚度及层中气体性质变化对缸内传热的影响，分析了陶瓷隔热发动机制工内的传热特性，并对其燃油消耗率上升，排温增高等原因，做出了合理的阐述。     

壁温对内燃机缸内传热影响的试验研究

提出了壁温对内燃机缸内瞬态传热的影响问题。在保证其它影响因素不变的条件下,利用作者研制出的一种特殊表面热电偶,成功地使壁温条件独立,并在一台点火式发动机上进行了试验。实测了不同壁面平均温度下的表面温度波动形态及在不同工况下表面温度波形的壁温特性与表面热流率的壁温特性。结果表明,壁面温度水平对传热特性确有影响,这种影响已显示出具有某种规律性。     

液压自由活塞发动机活塞运动规律自适应特性的研究

在一台液压自由活塞发动机(HFPE)样机上进行了活塞运动规率的试验。研究表明:活塞的运动规律对于燃烧相位和累积放热量的变动具有自适应性;随着燃烧相位的提前或累积放热量的增大,活塞换向提前,最大升程和压缩比降低;这种自适应性可有效避免均质压燃过程中的爆震与后燃现象,保证缸内最高压力、最大放热速率的稳定,减少指示功的损失。     

燃烧室壁面积炭层的形成及其对壁面瞬时温度和瞬时热流量的影响

在一台单缸柴油机上，通过采用着火前后倒拖工况运行，研究燃烧室壁面积层的形成及其随发动机运行工况，运行时间，燃烧室壁面位置等的变化规律，以及镀表面积炭层对测量壁面瞬时温度，瞬时热流量的影响。     

Simulation of the combustion process for a CI hydrogen engine in an argon-oxygen atmosphere

Hydrogen combustion in a noble gas atmosphere increases the combustion chamber temperature, and the high specific heat ratio of the gas increases the thermal efficiency. In this study, nitrogen was replaced by argon as the intake air along with pure oxygen to supply the engine. The objectives of this study are to determine the effects of different engine parameters on combustion and to analyse the emissions from hydrogen combustion in an argon-oxygen atmosphere. This research was conducted through simulations using CONVERGE 2.2.0 software, and the YANMAR engine NF19SK model was used to determine the basic parameters. Changing the injector location affects the pressure and temperature in the combustion chamber. With increasing compression ratio, the pressure increases more rapidly than the temperature. However, combustion at high compression ratios decreases the maximum heat release rate and increases the combustion duration. Hydrogen combustion at ambient temperatures below 1200 K follows the Arrhenius equation.     

燃油的喷射雾化燃烧对柴油机缸内空气流动影响的研究

将柴油机缸内气体与全体燃烧室部件(气缸盖-气缸套-活塞组)作为一个耦合体,在对耦合体进行传热数值模拟的基础上得到缸内流动计算的壁面边界条件。利用大型通用CFD软件STAR-CD及ES-ICE,在进气压缩过程流动三维瞬态数值模拟基础上,对6110柴油机喷雾燃烧过程缸内三维非稳态流动进行数值模拟研究,着重分析燃油喷射、雾化、燃烧对缸内流动的影响。研究结果表明喷雾燃烧过程中燃油的喷射流动直接影响到缸内流场的总流型,在一定空间内完全打破缸内大的旋流流场。     

Stoichiometric H2ICEs with water injection

For the most part, gasoline engines operate close to stoichiometry because of the high power density and the easy after treatment through the very well established three-way catalytic converter technology. The lean burn gasoline engine suffers major disadvantages for the after treatment still requiring aggressive research and development to meet future emission standards more than for the lower power density compensated by the better fuel conversion efficiency running lean. Hydrogen engines are usually run ultra-lean to avoid abnormal combustion phenomena and possibly to avoid the emission of nitrogen oxides without the difficult non-stoichiometric after treatment. While the ultra-lean combustion of hydrogen may reduce the formation of NOx within the cylinder but makes the power density very low, the only lean combustion of hydrogen requires after treatment for NOx reduction. The suppression of abnormal combustion in hydrogen engines has been a challenge for the three regimes of abnormal combustion, knock (auto ignition of the end gas region), pre-ignition (uncontrolled ignition induced by a hot spot prior of the spark ignition) and backfire (premature ignition during the intake stroke, which could be seen as an early form of pre-ignition). Direct injection and jet ignition coupled to port water injection are used here to avoid the occurrence of all these abnormal combustion phenomena as well as to control the temperature of gases to turbine in a turbocharged stoichiometric hydrogen engine.     

A cold‐start method and analysis for internal combustion engines particularly using a renewable fuel

A new cold‐start approach for internal combustion engines is described, which may be particularly suitable for an engine using an alternative fuel, such as ethanol or methanol. One of the cylinders in the engine may be equipped with a holding chamber in the cylinder head for the cold‐start purpose. The holding chamber may be opened or closed by a holding chamber valve to establish or block the fluid flow between the holding chamber and the cylinder space. The cold‐start procedure includes an intake stroke and a compression stroke, an expansion stroke that conserves the energy content of the earlier compressed charge without returning the compression work to the piston, and a subsequent recompression stroke to compress the charge to a much higher temperature. A thermodynamic analysis on the cold‐start process of a homogeneous charge internal combustion engine is undertaken, which includes the effect of fuel vaporization on the temperature change of the charge during the first compression stroke. It is found that the charge could be compressed effectively to a sufficiently higher temperature for ignition with pure ethanol as fuel. Copyright © 2010 John Wiley & Sons, Ltd.     

基于可变气门定时策略的HCCI汽油机试验研究

在电控气口喷射四冲程单缸试验机上,利用特殊设计的小包角配气凸轮,通过负气门重叠角实现了由内部残余废气控制的汽油HCCI燃烧,详细研究了气门定时参数对HCCI燃烧的影响.结果表明,就进排气门定时比较而言,排气门关闭时刻对内部EGR率和负荷的影响更大,而进气门开启时刻对HCCI燃烧的影响相对较小.在进排气门相位对称条件下,随着气门重叠负角的减小,最大压力升高率增加,着火时刻提前,负荷也增大.随着转速的增加,内部EGR率增加,排气温度升高,着火时刻也提前.通过调整气门定时,在不需要进气加热的条件下,可在转速880～4 000 r/min,负荷0.25～0.75 MPa（pIMEP）的范围实现HCCI燃烧.     

Comparative combustion characteristics of gasoline and hydrogen fuelled ICEs

In this paper, some models of comparative combustion characteristics for gasoline and hydrogen fuelled spark ignition internal combustion engines were developed and discussed from a thermodynamic and heat transfer perspective. The geometry used was that of a 3.4L GM V6 engine with a compression ratio of 9.5:1. Models for mass fraction burned, pressure, temperature, and gas speed were developed according to the literature survey and graphed over the cycle range. Furthermore, Pressure–Volume and Temperature–Entropy models were developed for both gasoline and hydrogen fuelled engines. Analysis of these models indicated approximately a 6.42% increase thermal efficiency for the hydrogen fuelled engine due to less exhaust blow down, less heat rejection during the exhaust stroke, and its shorter combustion duration closer to TDC. However, it was found that the hydrogen fuelled engine had approximately a 35.0% decrease in power output at an equivalence ratio of 1.0 due to the decrease in MEP and a greater amount of heat transfer to the cooling system due to the increased combustion temperatures, shorter quenching distance associated with H₂ combustion and greater flame speed. Finally, an increase in cycle temperatures and pressures was observed from increasing the equivalence ratio from 0.4 to 1.0 to 1.2.     

Experiments on the influence of intake conditions on local instantaneous heat flux in reciprocating internal combustion engines

The present study tries to be a contribution for the development of more precise theoretical models for predicting the dissipation of heat through the combustion chamber walls of reciprocating (internal combustion) IC engines. A fast response thermocouple was embedded in the combustion chamber of a single cylinder engine to measure instantaneous wall temperatures. The heat flux was obtained by solving the one-dimensional transient energy equation with transient boundary conditions using the Fast Fourier Transform. The engine was tested under different operating conditions to evaluate the sensitivity of the measurement procedure to variations of three relevant combustion parameters: injection pressure, air temperature and oxygen concentration at the intake. The local heat flux obtained was compared with other relevant parameters that characterize the thermal behaviour of engines, showing, in most of the cases, correlation among them. The results showed that the instantaneous heat flux through the walls and hence the local wall temperatures are strongly affected by the ignition delay and the start of combustion.     

Effect of hydrogen enrichment in the intake air of diesel engine fuelled with honge biodiesel blend and diesel

In the current investigation, the enrichment of hydrogen with the honge biodiesel blend and diesel is used in a compression ignition engine. The biodiesel is derived from the honge oil and mixed with diesel fuel by 20% (v/v). Thereafter, hydrogen at different volume flow rates (10 and 13 lpm) is introduced into the intake manifold. The outcomes by enrichment of hydrogen on the performance, combustion and emission characteristics are investigated by examining the brake thermal efficiency, fuel consumption, HC, CO, CO₂, NOₓ emissions, in-cylinder pressure, combustion duration, and rate of heat release. The engine fuelled with honge biodiesel blend is found to enhance the thermal efficiency, combustion characteristics. Compare to diesel, the BTE increased by 2.2% and 6% less fuel consumption for the HB20 + 13H₂ blend. Further, reduction in the emission of exhausts gases like CO and HC by 21% and 24%, respectively, are obtained. This is due to carbon-free structure in hydrogen. Moreover, due to high pressure in the cylinder, there is a slight increase in oxides of nitrogen emission compare to diesel. The combustion characteristics such as rate of heat release, combustion duration, and maximum ₂rate of pressure rise and in-cylinder pressure are high due to hydrogen.     

Study of the cycle-to-cycle variations of an internal combustion engine fuelled with natural gas/hydrogen blends from the diagnosis of combustion pressure

A methodology is presented for studying the influence of using alternative fuels on the cycle-to-cycle variations of a spark ignition engine which has been fuelled with mixtures of natural gas and hydrogen in different proportions (0–100%). The experimental facility consists of a single-cylindrical spark ignition engine coupled to an asynchronous machine with a constant engine rotation speed of 1500 rpm. A thermodynamic combustion diagnostic model based on genetic algorithms is used to evaluate the combustion chamber pressure data experimentally obtained in the mentioned engine. The model is used to make the pressure diagnosis of series of 830 consecutive engine cycles automatically, with a high grade of objectivity of the combustion analysis, since the relevant adjustment parameters (i.e. pressure offset, effective compression ratio, top dead center angular position, heat transfer coefficients) are calculated by the genetic algorithm. Results indicate that the combustion process is dominated by the turbulence inside the combustion chamber (generated during intake and compression), showing little dependency of combustion variation on the mixture composition. This becomes more evident when relevant combustion variables are plotted versus the Mass Fraction Burned of each mixture. The only exception is the case of 100% hydrogen, due to the inherent higher laminar speed of hydrogen that causes combustion acceleration and thus turbulence generation.