Applicability of heat transfer equations to hydrogen combustion

Previous research by the authors showed that hydrogen combustion exhibits a higher cooling loss to the combustion chamber wall of an internal combustion engine compared to hydrocarbon combustion because of its higher burning velocity and shorter quenching distance. The high cooling loss means that reduction of the cooling loss is essential to establish a high thermal efficiency in hydrogen combustion engines. This research analyzed the applicability of equations to describe the heat transfer from burning gases to hydrogen combustion. The result shows that equations calculate a lower cooling loss than experimental values, and the use of correction coefficients does not accurately define the actual cooling rate. It is therefore concluded that the derivation of a new heat transfer equation for hydrogen combustion is necessary to improve the thermal efficiency of hydrogen fuelled engines.     

Reduction of emissions with propane addition to a diesel engine

Recent studies on dual-fuel combustion in compression-ignition (CI) engines, also known as diesel engines, fall into two categories. In the first category are studies focused on the addition of small amounts of gaseous fuel to CI engines. In these studies, gaseous fuel is regarded as a secondary fuel and diesel fuel is regarded as the main fuel for combustion. The objectives of these studies typically involve reducing particulate matter (PM) emissions by using gaseous fuel as a partial substitution for diesel fuel. However, the addition of gaseous fuel raises the combustion temperature, which increases emissions of nitrogen oxides (NO_x). In the second category are studies focused on reactivity-controlled compression-ignition (RCCI) combustion. RCCI combustion can be implemented by early diesel injection with a large amount of low-reactivity fuel such as gasoline or gaseous fuel. Although RCCI combustion promises lower NO_x and PM emissions and higher thermal efficiency than conventional diesel combustion, it requires a higher intake pressure (usually more than 1.7 bars) to maintain a lean fuel mixture. Therefore, in this study, practical applications of dual-fuel combustion with a low air-fuel ratio (AFR), which implies a low intake pressure, were systemically evaluated using propane in a diesel engine. The characteristics of dualfuel combustion for high and low AFRs were first evaluated. The proportion of propane used for four different operating conditions was then increased to decrease emissions and to identify the optimal condition for dual-fuel combustion. Although the four operating conditions differ, the AFR was maintained at 20 (? approximately equal to 0.72) and the 50% mass fraction burned (MFB 50) was also fixed. The results show that dual-fuel combustion can reduce NO_x and PM emissions in comparison to conventional diesel combustion.     

Model based burnt gas fraction controller design of diesel engine with VGT/Dual loop EGR system

-Recently, regulation of NOx and PM emission in diesel engines has become stricter and the EGR system has been expanded into a dual loop EGR system to increase EGR rate as well as to utilize exhaust gas strategically. In terms of engine combustion characteristics, burnt gas fraction is becoming an important factor of solving the NOx and PM emission reduction problem more efficiently but conventional controller focused only pressure and air flow rate targets. Unlike the previous studies, this paper describes a model based burnt gas fraction control structure for a diesel engine with a dual loop EGR and a turbocharger. Feedforward control inputs based on burnt gas fraction states aids in the precise control of diesel engines, especially in transient states by considering coupled behavior within the system. For the controller validation, a control oriented reduced order model of a diesel engine air management system is established to simplify the control input computation and its stability is proved by analysing the internal dynamics stability. Then, a sliding mode controller is designed and controller robustness at certain operating points is validated using an HiLS bench.     

增压柴油机热负荷研究

增压发动机热负荷的增加会影响发动机的使用寿命。针对不同的与燃气直接接触的发动机零件。介绍了具体的测点布置方案及测试方法，并对CA6DFl-27型柴油机进行了实机试验。指出，CA6DFl-27型柴油机在现有功率下不能满足热负荷要求，宜采取各缸进水口位置上移的解决方法。通过对改进后发动机热负荷的测试可以看出。各测点的温度有明显的降低。     

Gasoline multiple premixed compression ignition (MPCI): Controllable, high efficiency and clean combustion mode in direct injection engines

A novel combustion concept namely “multiple premixed compression ignition” (MPCI) in gasoline direct injection compression ignition (GDICI) regime is proposed. Its predominant feature is the first premixed and followed quasipremixed combustion processes in a sequence of “spray-combustion-spray-combustion”. The multiple-stage premixed combustion decouples the pressure rise with pollutants formation process, which means the pressure rise rate and emissions can be reduced simultaneously, while achieving a high thermal efficiency. The gasoline MPCI mode has been demonstrated in a research engine with a compression ratio of 18.5. Gasoline with the research octane number (RON) of 94.4 was tested under 1400 rpm, 0.6 MPa IMEP conditions, without EGR and intake boosting. A parameter study of common rail pressure and intake temperature was implemented to investigate their effects on the performance of MPCI mode. Compared to the single-stage diffusion combustion in traditional diesel engines, the gasoline MPCI mode achieves lower emissions of soot, NO, CO, as well as slightly higher indicated efficiency, with a penalty of higher THC emissions when the common rail pressure is larger than 80 MPa in this study. With intake temperature sweeping, the gasoline MPCI mode also has the foregoing advantages compared to the diesel under the same operating conditions.     

Influence of turpentine addition in Jatropha biodiesel on CI engine performance,combustion and exhaust emissions

The prospect of using turpentine oil as an additive for Jatropha biodiesel and using it as an alternative fuel for diesel in CI engines has been experimented in this work. Tests were carried out in a single cylinder, air cooled, constant speed, direct injection diesel engine. The results display that the performance of Jatropha-Mineral Turpentine (JMT) and Jatropha- Wood Turpentine (JWT) blends were found close to diesel, emission features were enhanced and combustion parameters were noticed to be comparable with diesel. Brake thermal efficiency of JMT20 blend found closer to diesel at 75 % load. BSFC increases for JMT and JWT blends at part load and maintains at full load. CO, HC and Smoke emissions were reduced with JMT and JWT blends at 75 % load. NOx emissions were on the raise. Furthermore, JMT and JWT blends offered comparable performance and combustion parameters, reduced emissions and both can substitute standard diesel in CI engines.     

Heat loss to the combustion chamber wall with deposit in D.I. diesel engine: variation of instantaneous heat flux on piston surface with deposit

Adhesion of deposit on the combustion chamber walls affects the state of the heat loss into combustion chamber wall surfaces in the internal combustion engine. In this study, as the first step, the instantaneous surface temperature and the instantaneous heat flux were measured by thin film thermocouples on piston surfaces in the D.I. diesel engine with the adhesion of deposit in order to clarify the effects of deposit. As a result, it is found that the instantaneous surface temperature and heat flux strongly depend on the amount of deposit adhered to the combustion chamber wall surfaces.     

柴油机高压及微孔径下燃油雾化特性的数值研究(Ⅱ)——湍流模型对燃烧的影响

为了有效模拟燃油燃烧过程,向计算流体力学平台KIVA-3V中加入了大涡模拟程序,同时耦合了化学反应动力学软件Chemkin,建立了喷雾燃烧过程的大涡模拟燃烧平台。研究了在高压和微孔径条件下两种湍流模型对燃油雾化燃烧过程的影响,同时对1台Caterpillar 3401重型柴油发动机缸内燃油喷雾燃烧过程进行了数值研究。结果显示,大涡模拟得到的燃油的燃烧过程与试验结果较为接近,燃烧温度分布及缸内压力变化趋势都要好于雷诺平均模型。     

液化石油气／柴油双燃料发动机放热规律分析

利用CB366燃烧分析仪测录的液化石油气（LPG）／柴油双燃料发动机和原柴油机示功图，比较了LPG／柴油双燃料发动机和原柴油机的燃烧特性及负荷对二者的影响，分析了供油提前角、掺烧比两因素对最高燃烧压力、燃烧放热率、着火开始时刻等双燃料发动机燃烧特性的影响，得出了有关双燃料发动机燃烧特性的结论。     

Effect of Charge Density on Spray Characteristics,Combustion Process,and Emissions of Heavy-Duty Diesel Engines

In-cylinder charge density at top dead center is an important parameter of diesel engines and is influenced by intake pressure, intake temperature, and compression ratio. The effects of charge density on fuel spray, combustion process, and emissions were investigated by using a constant volume bomb and a heavy-duty diesel engine. Spray development resistance increased with the increase of the charge density in the constant volume bomb. It was found that short spray penetration was accompanied by a large spray cone angle in the former stage with high charge density. However, the equivalence ratio was lowered and the degree of homogeneity of the mixture was increased in the later stage owing to the rapid interaction of fuel and gas at a high mixing rate. Combining the first law of thermodynamics and the second law of thermodynamics for analysis, as the charge density increased, the gross indicated thermal efficiency (ITEg) was improved. However, pumping loss had to be considered with higher charge density. Under this condition, the brake thermal efficiency (BTE) trend was increased initially and decreased subsequently. Under high-load operation (1200 r/min BMEP, 2.0 MPa), the minimum charge density value of 44.8 kg/m³ was found to be reasonable. This charge density was suitable for combustion and brought about minimum exhaust energy and trade-off emissions. Moreover, by analyzing two operation conditions in terms of the maximum BTE with the Miller and the conventional cycles, compression temperature and combustion temperature were reduced in the Miller cycle with the charge density 44.8 kg/m³. A high C_p/C_v could improve the cylinder exergy/power conversion process by its positive effect of increasing the specific heat ratio. Owing to the interaction between a high C_p/C_v and exergy loss to heat transfer, the condition with the minimal charge density could produce more piston work.     

燃用乳化油的柴油机燃烧特性研究

通过对柴油机燃用O~#柴油和乳化油的示功图分析,用自编程序计算得到了放热规律曲线。对放热规律的3要素——开始放热时刻、放热规律曲线形状和燃烧持续时间进行了定量的比较分析。探讨了柴油机燃用乳化油的燃烧特点。     

Simulation of HCCI combustion with spatial inhomogeneities via a locally deterministic approach

There has been recent interest in a new engine type, Homogeneous Charge Compression Ignition (HCCI), to combine the advantages of SI and CI engines. In this paper, a locally deterministic approach is employed to consider spatial inhomogeneities using the KIVA-CHEMKIN package. Validation is performed for two experimental HCCI engines fueled, respectively, by hydrogen and n-heptane. The full mechanism for hydrogen and a skeletal mechanism for n-heptane are used for combustion chemistry. Differences in the reaction flow paths are shown at ignition and the heat release reaction stages of the two fuels. Results show good agreement between measured and calculated pressures for different initial mixture temperatures with estimated residual fractions. A parametric study is performed in both engines to consider the influences of the physical parameters wall temperature, swirl ratio and global equivalence ratio. The ignition time of n-heptane is shown to be relatively insensitive to variations in these parametric due to its two-stage ignition behavior.     

缸内直喷醇类燃料发动机的燃烧与排放特性

根据所测的示功图和排放,分析了一台采用火花点火、缸内直喷周向分层燃烧系统的发动机在燃用甲醇和乙醇时的性能和燃烧特性。研究表明,醇类燃料发动机的燃烧由预混燃烧与扩散燃烧组成,具有非常快的燃烧速率,而且非常稳定,ATDC(3°CA～6°CA)就燃烧完50%燃料,循环变动小于6%。与燃用乙醇相比,燃用甲醇时滞燃期较短,燃烧速率较快。由于采用分层燃烧,醇类燃料发动机具有与直喷柴油机相当的热效率,在负荷特性上,燃用醇类燃料时的NOx排放仅为柴油机的10%～40%,且能实现无烟燃烧,CO排放的增加低于1%,HC排放高于柴油机。     

Influence of the accelerating operation mechanism on the combustion noise in DI-diesel engines

This paper focuses on the mechanisms of combustion noise during the accelerating operation of multi-cylinder diesel engines using testing technology for the transient conditions of IC engines. Based on impact factors, such as the gas dynamic load and cylinder pressure oscillations, tests and analysis of the combustion noise during transient and steady-state conditions for different loads are made on four-cylinder naturally aspirated engines, turbocharged engines, EGR-introduced engines, and high pressure common rail engines. The laws of combustion noise difference for the same engine speed and load are researched during transient and steady-state conditions. It is found that during transient conditions, the maximum pressure rise rate and the high frequency oscillation amplitude of the cylinder pressure are all higher than those observed during steadystate conditions for the same engine speed and load. With their joint action, the combustion noise during transient conditions is greater than that during steady-state conditions. Turbocharging is useful in reducing the combustion noise during transient conditions. Turbocharging has a better effect on the control over the combustion noise during transient conditions with a constant engine speed and an increasing torque than in conditions with a constant torque and an increasing engine speed. One of the main reasons for different control effects on the combustion noise is that turbocharging causes different wall temperatures inside combustion chambers. The introduction of the appropriate EGR is helpful in the reduction of the combustion noise during transient conditions. The key to the control of combustion noise with EGR during transient conditions is whether a real-time adjustment to the EGR rate can be made to achieve the optimization of the EGR rates for different transient conditions. By means of analyzing the differences in the combustion noise between the transient and steady-state conditions for different pilot injection controls, we obtain a strategy for controlling the combustion noise during transient conditions with a pilot injection. Compared with the steady-state conditions, a larger pilot injection quantity and a longer interval between the main injection and pilot injection should be selected for transient conditions, and this is verified through tests.     

Modeling of flame-wall interaction for combustion and heat transfer in S.I. engines

A numerical combustion model was developed for an engine CFD code in spark ignition engine combustion chambers. The combustion model features the following new concepts: (1) The introduction of preheated reactants which are produced in the turbulent mixing process and consumed in the reaction process; (2) the modification of the probability of burned and unburned gas blobs meeting each other in consideration of a change in turbulence length scale, which becomes smaller in the near wall region. With the first concept, the model deals with turbulence-reaction controlled combustion in the near wall region as well as turbulence-controlled combustion in the core region. The second concept avoids the unrealistic flame shape due to the near wall acceleration of the turbulent flame propagation, which is inherently seen in combustion models based simply on the turbulent mixing time such as the Magnussen model. It is also shown that the present model gives more realistic local heat fluxes.     

Cooling effect of methanol on an n-heptane HCCI engine using a dual fuel system

Homogeneous charge compression ignition (HCCI) engines have the potential to raise the efficiency of reciprocating engines during partial load operation. However, the performance of the HCCI engine at high loads is restricted by severe knocking, which can be observed by the excessive pressure rise rate. This is due to the rapid combustion process occurring inside the cylinder, which does not follow the flame propagation that is seen in conventional engines. In this study, a low compression ratio of 9.5:1 for a gasoline engine was converted to operate in HCCI mode with the goal being to expand the stable operating region at high loads. Initially, pure n-heptane was used as the fuel at equivalence ratios of 0.30 to 0.58 with elevated intake charge temperatures of 180 and 90 °C, respectively. The n-heptane HCCI engine could reach a maximum performance at an indicated mean effective pressure (IMEP) of 0.38 MPa, which was larger than the performance found in the literature. To reach an even higher performance, a dual-fuel system was exploited. Methanol, as an anti-detonant additive, was introduced into the intake stream with various amounts of n-heptane at fixed equivalence ratios in the range of 0.42 to 0.52. It was found that the methanol addition cooled the mixture down prior to combustion and resulted in an increased coefficient of variation (COV). In order to maintain stable combustion and keep the pressure rise rate below the limit, the intake charge temperature should be increased. Introduction of 90% and 95% (vol/vol) hydrous methanol showed a similar trend but a lower thermal conversion efficiency and IMEP value. Therefore, a dual fuel HCCI engine could maintain a high thermal conversion efficiency across a wide load and enhance a 5% larger load compared to a pure n-heptane-fuelled HCCI engine. The hydrocarbon (HC) and carbon monoxide (CO) emissions were lower than 800 ppm and 0.10%, respectively. They were less at higher loads. The nitrogen oxides (NO _x ) emissions were below 12 ppm and were found to increase sharply at higher loads to a maximum of 23 ppm.     

Combustion phase detection algorithm for four-cylinder controlled autoignition engines using in-cylinder pressure information

For several decades, the primary goal of the automotive industry has been to reduce harmful emissions and improve fuel economy. Gasoline engines are clean and powerful propulsion systems, but have poorer fuel economy than that of diesel engines. However, due to the development of new technologies such as variable valve timing and lift and direct gasoline injection, controlled autoignition (CAI) combustion can be realized. CAI engines combine the advantages of cleaner emissions and lower fuel consumption than conventional spark-ignition gasoline engines. In this study, a cylinder-pressure-based combustion phase detection method for CAI combustion is proposed. This method utilizes a normalized difference pressure (NDP), which is defined as the normalized pressure difference between the firing and motoring in-cylinder pressures. The proposed method was developed and validated with steady-state experimental data from an inline 4 cylinder, 2 L gasoline direct injection (GDI) CAI engine. Because the calculations in the NDP method are faster and simpler than in the conventional combustion phase detection method in CAI engines, this method can be embedded in a real-time controller. Furthermore, the proposed method displayed good accuracy in detecting the combustion phase and thus stabilized CAI combustion. Finally, the detailed experimental results are presented.     

掺烧比对P50/甲醇双燃料发动机燃烧与排放的影响

燃料富氧重整和双燃料燃烧模式是改善燃烧过程和降低颗粒物排放的重要方法.在一台四缸增压中冷的高压共轨柴油机上,采用进气道喷射甲醇、缸内喷射P50(50％体积比例柴油与50％体积比例PODE)的双燃料模式,研究掺混比对P50/甲醇双燃料发动机燃烧与排放特性的影响.研究结果表明:相比于纯柴油模式,P50及P50/甲醇双燃料燃...     

车用柴油机微粒捕集器热再生的一维数值模拟

以壁流式蜂窝陶瓷微粒捕集器(DPF)为研究对象,建立了DPF一维热再生过程的数学模型。对陶瓷孔道内微粒(PM)的燃烧过程及其温度分布进行了模拟,结果表明,再生过程进行到一半时,DPF载体的温度达到最大值。设计时必须保证在此温度下DPF的载体壁面不会发生破裂,以免影响其正常工作。     

Effects of mixture stratification on HCCI combustion of DME in a rapid compression and expansion machine

Compression ignition of homogeneous charges in internal combustion (IC) engines is expected to offer high efficiency of DI diesel engines without high levels of NOx and particulate emissions. This study is intended to find ways of extending the rich limit of HCCI operation, one of the problems yet to be overcome. Exhaust emissions characteristics are also explored through analyses of the combustion products. DME fuel, either mixed with air before induction or directly injected into the combustion chamber of a rapid compression and expansion machine, is compressed to ignite under various conditions of compression ratio, equivalence ratio, and injection timing. The characteristics of the resulting combustion and exhaust emissions are discussed in terms of the rate of heat release computed from the measured pressure, and the concentrations of THC, CO, and NOx are measured by FT-IR and CLD. The experimental data to date show that operation without knock is possible with mixtures of higher equivalence ratio when DME is directly injected rather than when it is inducted in the form of a perfectly homogeneous fuel-air mixture. Although fuel injected early in the compression stroke promotes homogeneity of the DME-air mixture in the cylinder, it causes the mixture to ignite too early to secure good thermal efficiency and knock-free operation at high loads. Low temperature reactions occur at about 660K regardless of the fueling methods, fuel injection timing and equivalence ratio. The main components of hydrocarbon emissions turned out to be unburned fuel (DME), formaldehyde and methane.