The effect of the initial charge temperature under various injection timings on the second law terms in a direct injection SI hydrogen engine

In this study, the effect of the initial charge temperature on the second law terms under the various injection timings in a direct injection spark ignition hydrogen fuelled engine has been performed theoretically during compression, combustion and expansion processes of the engine cycle. The first law analysis is done by using the results of a three dimensional CFD code. The results show a good agreement with the experimental data. Also for the second law analysis, a developed in house computational code is applied. The results reveal that the indicated work availability is more affected by varying hydrogen injection timing in comparison with other second law terms. Also increasing the initial charge temperature causes the heat loss availability and exhaust gas availability be increased and indicated work availability, combustion irreversibility and entropy generation be decreased.     

Availability analysis of a coke oven gas fueled spark ignition engine

The current work investigates a coke oven gas fueled spark ignition (SI) engine from the perspective of the first and second laws in order to understand the energy conversion performance of fuels and achieve highly efficient utilization. A detailed energy and exergy analysis is applied to a quasi-dimensional two-zone spark ignition engine model which combines turbulence flame propagation speed model at 1500 rpm by changing gas fuel types, compression ratio, load and ignition timing. It was found that the irreversibility of methane is the maximum and that of syngas is the minimum among the three different fuels. The irreversibility in the combustion process of a coke oven gas fueled SI engine is reduced when the compression ratio or the throttle valve opening angle is increased and the ignition timing is delayed. Increasing the compression ratio and delaying the ignition timing can improve the first and second law efficiency and reduce the brake specific fuel consumption (BSFC). The power performance and fuel economy are good and the energy is also used effectively when the compression ratio is 11, the throttle angle is 90% and the ignition time is ?10° CA ATDC respectively.     

Hydrogen enrichment effects on the second law analysis of a lean burn natural gas engine

This paper presents a computational work aimed at investigating the effects of hydrogen addition on the exergy (or availability) balance in a lean burn natural gas spark ignition (SI) engine. A thermodynamic engine cycle simulation was extended to perform the exergy analysis. A zero dimensional, two-zone computational model of the engine operation was used for the closed part of the cycle. The results of the model were compared with experimental data to demonstrate the validation of the model. Exergetic terms, such as exergy transfer with heat, exergy transfer with work, irreversibilities, fuel chemical exergy, and total exergy, were computed based on principles of the second law. The exergetic (the second law) efficiency was also calculated. The results of exergy analysis show that increasing hydrogen content and lean burn have considerably affected the exergy transfers, irreversibilities and second law efficiency. With increasing hydrogen content, the irreversibility produced during combustion decreases, and the second-law efficiency sharply increases at near the lean limit.     

A computer simulation of hydrogen fueled spark ignition engine

The work reported here pertains to some of the computer simulation models developed for hydrogen fueled spark ignition (SI) engines. The engine combustion process is modeled by using a semi-empirical turbulent flame speed expression. This combustion model has been employed to account for the hydrogen-air combustion process over a wide range of stoichiometric variables for the Varimax engine operating at various speeds and compression ratios. Based on the computed results, graphs showing the variation of combustion crank angle and flame speed with fuel-air equivalence ratio, engine speed, compression ratio etc., have been plotted.     

高效车用汽油机的技术进步

论述了车用汽油机的应用现状及其节能的潜力。作为基本指导思想,由热力学基本公式分析得到了提高汽油机热效率的途径是提高压缩比、稀薄燃烧以及降低泵气损失,同时指出应提高燃烧等容度以及降低循环波动。介绍了在进气道喷射汽油机上采取的节能技术,如提高压缩比、VVT、米勒循环以及停缸等。回顾并分析了缸内直喷汽油机(GDI)的发展历程与现状,特别分析对比了稀燃GDI与当量比GDI的优劣。最后,介绍了基于GDI发动机进行的HCCI以及HCII燃烧研究,指出分层混合气与SICI组合燃烧方式是在HCCI核心思想上衍生出来的,可以有效拓宽HCCI运行范围。     

天然气掺氢发动机的性能研究

以台架试验的方法,对不同负荷与点火提前角下天然气掺氢发动机的经济性和排放特性进行了研究,试验中使用了掺氢比为0%～40%的天然气掺氢混合燃料。试验结果表明,随着掺氢比的增加,燃气消耗率呈降低趋势,发动机的经济性得到明显的改善;在不同负荷下,随着掺氢比的增加,NOx与CO的排放都呈增加趋势,CH4的排放呈降低趋势。掺氢比一定时,随着点火提前角和掺氢比的增加,NOx、CH4与CO排放都呈增加趋势,优化点火提前角可以改善天然气发动机的排放。     

Measurement of in-cylinder soot particles and their distribution in an optical HSDI diesel engine using time resolved laser induced incandescence (TR-LII)

Soot particles generated during combustion process in a single cylinder optical diesel engine were measured using time-resolved laser induced incandescence technique (TR-LII). Experimentally measured LII data were fitted with theoretically simulated LII data to determine the count median particle diameter and the geometric width of the particle size distribution. TR-LII signals were acquired simultaneously at two different wavelengths for crank angles in the range from 48.4° to 111.4° after top dead centre (aTDC) and for various engine operating conditions. Particle size was found to be dependent on the engine load but no significant change in particle sizes were observed for different fuel injection timings. The average size of the primary particles measured over different crank angles were larger at higher engine loads compared to lower engine loads. A general trend of the soot particle diameter decreasing with crank angle was observed due to oxidation, but towards the end of the expansion stroke a marginal increase in size was noted. For all operating conditions the width of the particle size distribution was found to decrease with crank angle until 61.4°aTDC, and thereafter it increases to reach a well defined size distribution for a given fuel injection quantity despite the differences in the injection timing. The soot particles are randomly transported by the complex fluid motion present within the combustion chamber leading to strong cycle to cycle fluctuations of the measured time resolved LII data. The in-cylinder soot volume fraction derived from TR-LII data revealed that for different fuel injection timings, a relatively higher amount of soot was produced for shorter ignition delay compared to larger ignition delays.     

Theoretical investigation of flame propagation process in an SI engine running on gasoline–ethanol blends

Turbulent flame propagation process in a spark-ignition (SI) engine is theoretically investigated. Fueling with gasoline, ethanol and different gasoline–ethanol blends is considered. A quasi-dimensional SI engine cycle model previously developed by the author is used to predict the thermodynamic state of the cylinder charge during the cycle. The flame is assumed to be spherical in shape and centered at the spark plug. Computations are carried out for an automobile SI engine having a disc-shaped combustion chamber, for which the compression ratio and the nominal speed are 9.2 and 5800 rpm, respectively. Geometrical features (flame radius, flame front area and enflamed volume) of the flame, combustion characteristics (mass fraction burned and burn duration), and cylinder pressure and temperature are predicted as a function of the crank angle. Three different positions of the crank angle are studied: −10°, TC and +10°. It was concluded that ethanol addition to gasoline up to 25 vol% accelerated the flame propagation process.     

S195柴油机燃用纯甲醇、采用多火花助燃的研究

本文介绍了在S 195柴油机上燃用纯甲醇、采用多火花助燃的研究结果。选取合适的火花塞电极间隙、电极间隙与喷注空间匹配和正确的喷油、点火定时是保证非均相可燃混合气可靠着火燃烧的关键。当优化了上述参数后,发动机能在广阔的转速、负荷范围内稳定运行。燃用纯甲醇的柴油机与燃用柴油时热效率接近,并能实现无烟燃烧。试验表明,这种高压缩比、强涡流的柴油机对多火花点火系统有更好的适应性。     

火花点火激发均质压燃(SICI)组合燃烧的试验研究

均质混合气压燃(HCCI)燃烧高负荷拓展是内燃机燃烧领域的一个难题.在缸内直喷汽油机(GDI)上采用EGR、火花点火和可变配气技术来控制缸内混合气形成和燃烧,实现了3种燃烧方式:HCCI、火花点火激发均质压燃(SICI)组合燃烧方式、火花点火(SI)燃烧方式,研究了不同EGR率和点火提前角对SICI燃烧排放特性的影响.结果表明,汽油SICI组合燃烧方式呈现明显的两阶段燃烧特性,调整点燃放热比例可以实现HCCI燃烧向高负荷拓展(最大平均有效压力为0.82 MPa),同时能获得较低的NOx排放和高的热效率.     

乙醇/汽油双燃料双直喷模式下分层稀薄燃烧试验研究

针对乙醇与汽油固定掺混比例下使用不能充分发挥乙醇燃料优势的问题,开发出了乙醇汽油双燃料-双直喷系统,并在一台点燃式单缸试验机上进行试验,研究了稀薄燃烧下3种不同的喷射策略对发动机燃烧和性能的影响。研究发现:在稀薄燃烧的情况下,随喷射时刻的推迟,不同喷射策略下动力性呈现先增长后降低的趋势。在保证喷油量不变时,有效热效率随过量空气系数增大而明显提高,当量燃油消耗率逐渐降低。随喷射时刻的推迟,热效率呈现先升高后降低的趋势。在过量空气系数为1.2,汽油喷射时刻为上止点前180°,乙醇喷射时刻为上止点前300°时,有效热效率达到最高值40.5%。此外,相比于汽油,添加乙醇燃料使得稀薄燃烧更稳定,循环波动更小。     

Exergy destruction during the combustion process as functions of operating and design parameters for a spark‐ignition engine

The second law of thermodynamics provides different perspectives compared with the first law, and provides the property exergy. Exergy is a measure of the work potential of energy from a given thermodynamic state. Unlike energy, exergy may be destroyed, and for reciprocating engines, the major source of this destruction is during the combustion process. This paper provides an overview of the quantitative levels of exergy destruction during the combustion process as function of engine operating and design parameters, and for eight fuels. The results of this study are based on a spark‐ignition, automotive engine. The amount of exergy destroyed during the combustion process has been determined as functions of speed, load, equivalence ratio, start of combustion, combustion duration, combustion rate parameters, exhaust gas recirculation (EGR), inlet oxygen concentration, and compression ratio. In addition, design parameters that were examined included expansion ratio and the use of turbocharging. The fuels examined included isooctane (base), methane, propane, hexane, methanol, ethanol, hydrogen and carbon monoxide. For the part load base case (1400 rpm and a bmep of 325 kPa) using isooctane, the destruction of exergy was 20.8% of the fuel exergy. For many of the engine operating and design parameter changes, this destruction was relatively constant (between about 20 and 23%). The parameters that resulted in the greatest change of the exergy destruction were (1) equivalence ratio, (2) EGR, and (3) inlet oxygen concentration. For the base case conditions, the exergy destruction during the combustion process was different for the different fuels. The lowest destruction (8.1%) was for carbon monoxide and the highest destruction (20.8%) was for isooctane. The differences between the various fuels appear to relate to the complexity of the fuel molecule and the presence (or absence) of an oxygen atom. Copyright © 2011 John Wiley & Sons, Ltd.     

丙烷发动机燃烧变动研究

测量了火花点火丙烷气体发动机在不同转速、涡流强度及混合比下的气缸压力,并对测量的气缸压力及由气缸压力求出的用曲轴转角表示的初期燃烧期间等进行了统计分析。试验结果表明,随着混合气变稀平均指示压力的变动迅速增大;转速相同时,平均指示压力的变动随着涡流比的增大而减小;在稀薄混合气条件下,随着初期燃烧期间平均值的增加平均指示压力的变动急剧上升。     

The effect of hydrogen on the performance and emissions of an SI engine having a high compression ratio fuelled by compressed natural gas

The aim of this paper is investigation of the effect of hydrogen on engine performance and emissions characteristics of an SI engine, having a high compression ratio, fuelled by HCNG (hydrogen enriched compressed natural gas) blend. The experiments were carried out at 1500, 2000 and 2500 rpm under full load conditions of a modified Isuzu 3.9 L engine, having a compression ratio of 12.5. The engine brake power, brake thermal efficiency, combustion analysis and emissions parameters were realized at 5, 10 15 and 20 deg. CA BTDC (crank angle before top dead center) ignition timings and in excess air ratios of 0.9–1.3 fuelled by hydrogen enriched compressed natural gas (100/0, 95/5, 90/10 and 80/20 of % natural gas/hydrogen).The experimental results showed that the maximum power values were generally obtained with HCNG5 (5% hydrogen in natural gas) fuel. The optimum ignition timing that was obtained according to the maximum brake torque was retarded by the addition of hydrogen to CNG (compressed natural gas), while it was advanced by increasing the engine speed. Furthermore, it was observed that the BTE (brake thermal efficiency) generally declined with the hydrogen addition to compressed natural gas and increasing the engine speed. Additionally, the curves of cylinder pressure and ROHR (rate of heat release values) generally closed to top dead center with the increasing of the hydrogen fraction in the blend and a decreasing engine speed. The hydrocarbon and carbon monoxide emissions generally obtained were lower than the Euro-5 and Euro-6 standards.     

多孔介质发动机工作过程单区模型模拟

采用单区燃烧模型模拟多孔介质（PM）发动机的压缩、燃烧和膨胀过程。以热力学第一定律为基础,引入多孔介质换热模型,建立了多孔介质发动机的能量方程。计算了多种工况参数下PM发动机缸内温度、压强变化规律,分别讨论了压缩比、过量空气系数、多孔介质温度、多孔介质体换热系数等参数对多孔介质发动机燃烧过程的影响。将PM发动机与传统发动机加以比较,结果表明PM使缸内温度和压强的变化趋于平缓,这有利于混合气着火并可降低NO,排放。     

Numerical analysis of performance and emissions behavior of a bi-fuel engine with compressed natural gas enriched with hydrogen using variable compression ratio strategy

The increase in the compression ratio reduces the fuel consumption and improves the performance. These effects of compression ratio could be observed in all of the engines, such as compression or spark ignition engines. Moreover, due to the compression ratio constraint based on the knocking phenomenon in spark ignition engines, there will always be an optimal compression ratio, which is one of the most fundamental factors in engine design. The optimum compression ratio could be achieved depending on the type of fuel, but in the case of bi-fuel engines, since the nature of each fuel is different, the design must be relatively optimal for both fuels. In this work, by using the VCR (variable compression ratio) strategy, the bi-fuel EF7 engine performance, combustion, and emissions were investigated in different compression ratios when the engine uses gasoline or HCNG (hydrogen enriched compressed natural gas) as fuel. The results revealed that by changing the compression ratio from 11.05 (actual compression ratio of engine) to 11.80 in HCNG mode, an increase of 13% in power could be achieved. Also CO formation, at the compression ratio of 11.80, was slightly lower (7%) than the compression ratio of 11.05. In addition, by reducing the compression ratio from 11.05 to 10.50 in gasoline mode, there was a significant increase in emissions; that was 44% for the NO_x and 16% for the CO, which could be one of the limiting factors of the advance in spark timing. Moreover, due to the VCR strategy and the significant optimization of the compression ratio, the combinatory method of VCR – HCNG can be used as an effective method for the bi-fuel engines in order to improve the performance and reduce emissions.     

Comparative first- and second-law parametric study of transient diesel engine operation

A computer model is developed for studying the first- and second-law (availability) balances of a turbocharged diesel engine, operating under transient load conditions. Special attention is paid to the direct comparison between the results from the two laws, for various operating parameters of the engine. The model simulates the transient operation on a degree crank angle basis, using a detailed analysis of mechanical friction, a separate consideration for the processes of each cylinder during a cycle (“multi-cylinder” model) and a mathematical model of the fuel pump. Experimental data taken from a marine duty, turbocharged diesel engine, located at the authors’ laboratory, are used for the evaluation of the model's predictive capabilities. The first-law (e.g., engine speed, fuel pump rack position, engine load, etc.) and second-law (e.g., irreversibilities, heat loss and exhaust gases) terms for the diesel engine cylinder are both computed and depicted in comparison, using detailed diagrams, for various engine operating parameters. It is revealed that, at least for the specific engine type and operation, a thermodynamic, dynamic or design parameter can have a conflicting impact on the engine transient response as regards energy and availability properties, implying that both a first- and second-law optimization is needed for best performance evaluation.     

高压直喷点燃式发动机燃用航空煤油掺混乙醇对燃烧性能优化的试验研究

为提高航空煤油在点燃式发动机中的燃烧热效率,改善发动机爆震及拓宽发动机负荷范围,以3号航空煤油(RP3)为基础燃料,以乙醇为辅助燃料,基于一台单缸水冷、压缩比可调、四冲程点燃式发动机结合高压共轨缸内直喷技术,开展了不同负荷、不同乙醇和航空煤油掺混比、不同喷射压力、不同喷射时刻下航空煤油燃烧特性的试验研究。结果表明,在压缩比为7的条件下,由于爆震的限制,发动机负荷仅能达到原机的72.0%。而乙醇具有较强的抑制爆震的能力,随着乙醇在航空煤油中掺混比例的增加,发动机负荷区间不断拓展,当乙醇的掺混比为10%时发动机可实现全负荷工作。继续增大乙醇的掺混比例,可进一步提升功率并降低油耗。为探究喷油时刻对动力性、经济性的影响,试验测定了5种喷油时刻对燃烧性能的影响。当喷油时刻为压缩上止点前300°时,发动机具有较好的动力性;当喷油时刻为上止点前360°时,发动机具有较好的经济性。     

Thermodynamic analysis and utilisation of wet ethanol in homogeneous charge compression ignition engine

In this study, our objective is to computationally analyse the wet ethanol operated homogeneous charge compression ignition (HCCI) engine to evaluate its first and second law efficiency and observe these results by varying effectiveness of regenerator. The paper concludes that the first and second law efficiency decreases due to the increase in the effectiveness of regenerator. This increase in effectiveness leads to an increase in the temperature of air coming out of the regenerator. It further results in increase of the fuel air mixture intake temperature which finally reduces the work output and efficiency of the engine. Furthermore, the method of exergy analysis has been applied and evaluated. This study indicates that due to domination of chemical exergy destruction in combustion reaction in these systems, maximum exergy is destroyed in HCCI engine and to a lesser extent in catalytic converter. These findings will help in the design of such system for optimum result.     

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.