Effect of air injection on the characteristics of transient response in a turbocharged diesel engine

An experimental study was performed to investigate the improvement of transient characteristics of a turbocharged diesel engine under the conditions of low speed and fast acceleration with the load. In this study, the experiment for improving the low speed torque and acceleration performance is performed by means of injecting air into the intake manifold during the period of low speed and application of a fast acceleration. The effects of air injection into the intake manifold on the response performance are investigated at various thermodynamic parameters such as air injection pressure, air injection period, accelerating rate, accelerating time, engine speed and load. The experimental results show that air injection into the intake manifold at compressor exit is closely related to the improvement of low speed and acceleration performance of a turbocharged diesel engine. During the rapid acceleration period, the air injection into the intake manifold of turbocharged diesel engine indicates the improvement of the combustion characteristics and gas pressure in the cylinder. At low speed range of the engine, the effect of air injection shows the improvement of the pressure distribution of turbocharger and combustion pressure during the period of gas exchange pressure.     

Experimental study of combustion noise radiation during transient turbocharged diesel engine operation

Diesel engine noise radiation has drawn increased attention in recent years since it is associated with the passengers’ and pedestrians’ discomfort, a fact that has been acknowledged by the manufacturers and the legislation in many countries. In the current study, experimental tests were conducted on a truck, turbocharged diesel engine in order to investigate the mechanism of combustion noise emission under various transient schedules experienced during daily driving conditions, namely acceleration and load increase. To this aim, a fully instrumented test bed was set up in order to capture the development of key engine and turbocharger variables during the transient events. Analytical diagrams are provided to explain the behavior of combustion noise radiation in conjunction with cylinder pressure (spectrum), turbocharger and governor/fuel pump response. Turbocharger lag was found to be the main cause for the noise spikes during all test cases examined, with the engine injection timing calibration and the slow adjustment of cylinder wall temperature to the new fueling conditions playing a vital role. The analysis was extended with a quasi-steady approximation of transient combustion noise using steady-state maps, in order to better highlight the effect of dynamic engine operation on combustion noise emissions.     

Experimental investigation of the performance and exhaust emissions of a swirl chamber diesel engine using JP-8 aviation fuel

An experimental study is conducted to evaluate the use of JP-8 aviation fuel as a full substitute for diesel fuel in a Ricardo E-6 high-speed naturally-aspirated four-stroke experimental engine having a swirl combustion chamber. The study covers a wide range of engine load and speed operating conditions, comprising measurements of cylinder pressure diagrams, high-pressure fuel pipe pressures, exhaust gas temperatures, fuel consumptions, exhaust smokiness and exhaust gas emissions (nitrogen oxides, unburned hydrocarbons and carbon monoxide). Processing of the measurements provides important performance parameters such as maximum combustion pressure, dynamic injection timing, ignition delay, combustion irregularity and knocking tendency. The differences in the measured performance and exhaust emission parameters are determined for engine operation with JP-8 fuel, against baseline engine operation using diesel fuel. The study shows that the exhaust emission levels are not much different for operation with the two fuels. On the contrary, operation with JP-8 fuel increases combustion pressures, combustion intensity and irregularity. This is caused mainly by high pressure fluctuations present in the fuel injection system due to the different physical properties of JP-8 fuel (compared to diesel fuel), which totally change the injection characteristics. Retardation of the static injection timing is one means of improving this situation, while using the same fuel injection equipment. © 1997 John Wiley & Sons, Ltd.     

Availability analysis of a turbocharged diesel engine operating under transient load conditions

A computer analysis is developed for studying the energy and availability performance of a turbocharged diesel engine, operating under transient load conditions. The model incorporates many novel features for the simulation of transient operation, such as detailed analysis of mechanical friction, separate consideration for the processes of each cylinder during a cycle (“multi-cylinder” model) and mathematical modeling of the fuel pump. This model has been validated against experimental data taken from a turbocharged diesel engine, located at the authors’ laboratory and operated under transient conditions. The availability terms for the diesel engine and its subsystems are analyzed, i.e. cylinder for both the open and closed parts of the cycle, inlet and exhaust manifolds, turbocharger and aftercooler. The present analysis reveals, via multiple diagrams, how the availability properties of the diesel engine and its subsystems develop during the evolution of the engine cycles, assessing the importance of each property. In particular the irreversibilities term, which is absent from any analysis based solely on the first-law of thermodynamics, is given in detail as regards transient response as well as the rate and cumulative terms during a cycle, revealing the magnitude of contribution of all the subsystems to the total availability destruction.     

某大功率柴油机推进动力模块动态特性研究

以某型16缸大功率增压柴油机动力模块为研究对象,采用AMESim软件建立了柴油机动力模块的仿真模型,并通过试验数据对仿真模型进行了标定.基于该模型对柴油机推进动力模块加速过程中模块转速与设定值的偏差,以及瞬态调速过程中模块带大惯量运行的规律以及喷油控制优化进行了仿真研究.研究结果表明:减小涡轮增压器惯量可以优化柴油机加...     

柴油机冷却水套空化两相流三维瞬态数值模拟研究

为了深入研究柴油机湿式气缸套振动引发穴蚀的机理和影响因素,在水套内部冷却液流动稳态数值模拟得到冷却液压力场与速度场的基础上,以完整单缸水套为研究对象,提取6缸稳态模拟结果作为边界条件.基于Mixture多相流模型与Singhal完全空化模型,采用动网格技术建立柴油机冷却液空化数值模拟的气液两相流仿真模型,进行冷却液空化...     

Lubricating oil effects on the transient performance of a turbocharged diesel engine

The modeling of transient turbocharged diesel engine operation appeared in the early seventies and continues to be in the focal point of research, due to the importance of transient response in the everyday operating conditions of engines. The majority of research has focused so far on issues concerning thermodynamic modeling, as these directly affect performance and pollutants' emissions. On the other hand, issues concerning the dynamics of transient operation are usually over-simplified, possibly for the sake of speeding up program execution time. In the present work, an experimentally validated transient diesel engine simulation code is used to study and evaluate the importance of the lubricating oil properties (oil-type, viscosity, temperature) on the transient response of a turbocharged diesel engine. It is revealed how the lubricating oil affects mechanical friction and hence, the speed response as well as the other interesting parameters, e.g. fuel pump rack position or turbocharger operating point for load-change schedules typical in the European Transient Cycles for heavy-duty engines. Particularly under low ambient conditions, the high oil viscosity is responsible for a significant increase in the respective frictional losses worsening the engine transient response.     

提高重型柴油机低速高负荷热效率的试验研究

为了改善重型柴油机低速高负荷的燃油经济性,在一台两级可变截面涡轮增压重型柴油机上开展了空气系统与喷油参数优化策略研究。试验结果表明:对于缸内最高燃烧压力受限工况,获得最低有效燃油消耗率(BSFC)的可变截面涡轮增压器(VGT)关度应该使泵吸功基本为零;选取合适的喷油压力可提高机械效率,在改善燃油经济性的同时使NO_x排放有一定降低,而碳烟排放也能保持在较低水平。基于该优化策略,研究了缸内最高燃烧压力限值对不同工况点燃油经济性的影响,进而研究了提高缸内最高燃烧压力对改善燃油经济性的潜力。结果表明:随着转速与负荷的升高,提高最高燃烧压力限值对燃油经济性的改善作用更加明显;但缸内最高燃烧压力提高到一定程度以后,其对燃油经济性的改善作用逐渐减小。     

直喷式柴油机起动过程燃烧分析

为了快速、定性分析柴油机起动过程中的燃烧状态,在直喷式柴油机上进行冷机与热机起动过程实验,提出用瞬时转速和示功图对柴油机起动进行燃烧分析的方法．实验结果表明,冷机起动过程中有失火现象,用瞬时转速可以判断着火首循环和失火循环．根据示功图形状及燃烧状态,定义了4种燃烧状态以及相对应的4种典型示功图形式,将起动过程划分为4个阶段．热机起动初始期和过渡期很短,而冷机起动有明显的4个阶段．不完全燃烧或失火是柴油机起动过程、燃烧过程控制优化的重点,多出现在起动初始期和过渡期．     

Experimental study of the interactions between long and short-term unsteady heat transfer responses on the in-cylinder and exhaust manifold diesel engine surfaces

The paper presents the results from the analysis of an experimental investigation with the aim to provide insight to the cyclic, instantaneous heat transfer phenomena occurring in both the cylinder head and exhaust manifold wall surfaces of a direct injection (DI), air-cooled diesel engine. The mechanism of cyclic heat transfer is investigated during engine transient events, viz. after a sudden change in engine speed and/or load, both for the combustion chamber and exhaust manifold surfaces. These results are then compared with relevant experimental data from steady state operation which in the present case are used as reference helping to reveal any potential influences of each transient event on cyclic heat transfer. The experimental installation allowed both long- and short-term signal types to be recorded on a common time reference base during the transient event. Processing of experimental data was accomplished using a modified version of one-dimensional heat conduction theory with Fourier analysis, capable to cater for the special characteristics of transient engine operation. Based on this model, the evolution of local surface heat flux during a transient event was calculated. Two engine transient events are examined, which present a key difference in the way the load and speed changes are imposed on each one of them. From the analysis of experimental results it is confirmed that each thermal transient event consists of two distinguished phases the “thermodynamic” and the “structural” one which are appropriately configured and analyzed. In the case of a severe variation, in the first 20 cycles after the beginning of the transient event, the wall surface temperature amplitude on cylinder head was almost three times higher than the one observed at the “normal” temperature oscillations occurring during the steady state operation. At the same time, peak pressure values in the same cycles are increased by almost 15% above their corresponding values at the final steady state. The same phenomena are valid for the exhaust manifold surfaces but on a moderated scale.     

Combustion of jojoba methyl ester in an indirect injection diesel engine

An experimental investigation has been carried out to examine for the first time the performance and combustion noise of an indirect injection diesel engine running with new fuel derived from pure jojoba oil, jojoba methyl ester, and its blends with gas oil. A Ricardo E6 compression swirl diesel engine was fully instrumented for the measurement of combustion pressure and its rise rate and other operating parameters. Test parameters included the percentage of jojoba methyl ester in the blend, engine speed, load, injection timing and engine compression ratio. Results showed that the new fuel derived from jojoba is generally comparable and good replacement to gas oil in diesel engine at most engine operating conditions, in terms of performance parameters and combustion noise produced.     

The effect of elevated fuel inlet temperature on performance of diesel engine running on neat vegetable oil at constant speed conditions

The concept that engine design is all important in the use of vegetable oils as a diesel fuel has been pointed out by many researchers. One hundred percent of vegetable oil can be used safely in an indirect injection engine, but not in a direct injection engine due to the high degree of atomization required for this type. This problem is related to increasing droplet size on injection into the cylinder that results in poor combustion. This in turn, causes the formation of deposits in the combustion chamber, together with oil dilution due to introduction of unburnt fuel into the crankcase. The objective of this work was to evaluate the effect of increasing fuel inlet temperature on viscosity and performance of a single cylinder, unmodified diesel engine. The overall results showed that fuel heating increased peak cylinder pressure and was also beneficial at low speed and under part-load operation. The high combustion temperature at high engine speed becomes the dominant factor, making both heated and unheated fuel to acquire the same temperature before fuel injection.     

VNT可变涡轮增压器与柴油机的匹配研究

根据一款WG增压柴油机原机的基本结构参数和试验数据,匹配一款VNT废气涡轮增压器,建立VNT增压柴油机的GT-Power一维计算模型,并对柴油机外特性工况和ESC工况进行仿真计算研究。分别以动力性和经济性参数为分析指标,对外特性工况和ESC工况的VNT开度进行优化选择。研究表明,开度优化选择后的VNT柴油机与柴油机原机相比,外特性转矩均有较大幅度提高,最大转矩工况的运行范围拓宽,且VNT增压器的转速在整个转速范围内提高,联合运行曲线的高效率范围扩展;ESC工况加权比油耗值下降幅度约为3.8%,且空燃比增大,VNT柴油机经济性获得提升。可以得出结论,VNT可变涡轮增压器与柴油机匹配良好。     

过渡工况下风冷内燃机气缸盖温度的变化规律

在起动、突加和突减三种最苛刻的过渡工况下，对一台小型风冷内燃机气缸盖的非稳态温度进行了测量。试验分析了过渡工况下风冷内燃机气缸盖温度的变化规律，以便为有限元计算非稳态温度场提供真实的边界条件，并为进一步考察非稳态热负荷状况提供依据。     

Experimental evaluation of local instantaneous heat transfer characteristics in the combustion chamber of air-cooled direct injection diesel engine

An experimental analysis is conducted investigating the differences between the variations of overall and local instantaneous heat transfer coefficients, during the engine cycle, in the combustion chamber walls of a direct injection (DI), air-cooled diesel engine located at the authors’ laboratory. For this purpose, a novel experimental installation is developed, which separates the engine transient temperature signals into two parts, namely the long- and the short-term response ones, processed in two independent data acquisition systems. Moreover, a new pre-amplification unit for fast response thermocouples, appropriate heat flux sensors and an object-oriented control code for fast data acquisition have been designed and applied. Experimentally obtained cylinder pressure diagrams are used as a basis for the calculation of the overall heat transfer coefficients, whereas one-dimensional heat conduction theory with Fourier analysis techniques, combined with an iterative procedure between calculated and measured temperature data, are implemented in order to calculate the instantaneous local heat transfer coefficients in the engine cylinder. Analysis of the experimental results reveals interesting aspects of transient engine heat transfer. Significant differences are disclosed between the overall and local heat transfer coefficient variations, with the importance of the latter one on engine design being emphasized. The local heat transfer coefficient on the cylinder head is quantified based on the experimental data. The effect of engine speed and load as well as of the air swirling motion on the heat transfer variations are presented. From the analysis results it is concluded that the instantaneous heat transfer variation is non-uniform, unlike its values calculated from standard correlations that assume spatial uniformity, noting that such information, especially for air-cooled diesel engines, seems to be very scarce in the open literature.     

进气涡流对车用直喷式柴油机瞬态工况下微粒排放的影响

用自行设计的喷气式可变涡流进气系统（ＡＩＶＳＩＳ）调节气缸内的涡流水平,试验研究了进气涡流对车用直喷式柴油机恒转速增转矩瞬态工况下微粒排放的影响,结果表明,对于一定涡流比的瞬态工况,随着转矩变化率的增大,柴油机的微粒排放量逐渐增加,涡流比越小,瞬态工况微粒的排放随转矩变化率增大的速率越高。相同转矩增长率的瞬态工况,随着涡流比的增大,柴油机微粒的排放量逐渐降低。提高恒转速增转矩瞬态工况缸内的涡流强度     

Study of the steady and transient temperature field and heat flow in the combustion chamber components of a medium speed diesel engine using finite element analyses

The present work describes the development of a model for the calculation of the temperature field and heat flow in the combustion chamber components of internal combustion piston engines, which occur both under steady and transient engine operating conditions. Two and three-dimensional finite-element analyses were implemented for the representation of the complex geometry metal components (piston, liner and cylinder head). The model is applied for the piston and liner of a medium speed diesel engine, for which relevant experimental data exist in the literature. Special care is given for accurately specifying the thermal boundary conditions (temperatures and heat transfer coefficients). Gas side boundary conditions are calculated using a thermodynamic cycle simulation code, including spatial variation of the gas side heat transfer coefficient. Coolant sides (water on the external liner surface and oil on the piston undercrown surface) boundary conditions are calculated using correlations pertaining to real engine conditions. Also an effort is made to model the piston-ring belt-liner complex thermal paths using equivalent thermal circuits. A satisfactory degree of agreement is found between theoretical predictions and experimental measurements, revealing that the finite-element methods presented are successful in formulating this kind of problem, giving accurate results with reasonable computational cost. The utilization of the model reveals very clearly the essential role of engine operating transients (sudden changes in speed and/or load) in the generation of sharp temperature excursions in the metal components until a new steady state is reached. The phenomenon should be taken into account for correct engine design and safe operation (i.e. the avoidance of high local stresses).     

2缸高压共轨柴油机增压器性能匹配与研究

针对一款2缸高压共轨4气门增压柴油机,基于2缸柴油机进、排气压力波动的特殊性,研究了不同发火顺序的发动机排气对增压器匹配的影响,选择了360°CA的发火顺序,分析了2缸柴油机增压器效率的波动及泵气损失的特点。兼顾乘用车对柴油机高低速性能的要求,设计了2种方案的增压器进行分析和匹配试验,提出了增压器的改进优化技术措施并进行了优化试验。试验结果表明:柴油机中低速性能得到了改善,低速扭矩增加了8N.m,燃油消耗率降低了12g/(kW.h),柴油机的各项性能指标满足设计目标,排放达到欧Ⅳ标准。     

旁通补燃系统改善柴油机外特性的仿真研究

利用GT-POWER软件的仿真计算,研究了6缸V型柴油机上增加旁通补燃系统对发动机与增压器匹配性能的影响.仿真计算表明：旁通补燃系统可以改善柴油机在低转速时涡轮增压器的效率,是一种改善动态工况下增压器与发动机匹配的有效措施.     

Investigation of the temperature oscillations in the cylinder walls of a diesel engine with special reference to the limited cooled case

This work investigates the interesting phenomenon of the temperature (cyclic) oscillations in the combustion chamber walls of a diesel engine. For this purpose, a comprehensive simulation code of the thermodynamic cycle of the engine is developed taking into account both the closed and the open parts of it. The energy and state equations are applied, with appropriate combustion, gas heat transfer, and mass exchange with the atmosphere sub‐models, to yield cylinder pressure, local temperatures and heat release histories as well as various performance parameters of the engine. The model is appropriately coupled to a wall periodic conduction model, which uses the gas temperature variation as boundary condition throughout the engine cycle after being treated by Fourier analysis techniques. It is calibrated against measurements, at various load and speed conditions, from an experimental work carried out on a direct injection (DI), naturally aspirated, four‐stroke, diesel engine located at the authors' laboratory, which has been reported in detail previously. After gaining confidence into the predictive capabilities of the model, it is used to investigate the phenomenon further, thus providing insight into many interesting aspects of transient engine heat transfer, as far as the influence that engine wall material properties have on the values of cyclic temperature swings. These swings can take prohibitive values causing high wall thermal fatigue, when materials of specific technological interest such as thermal insulators (ceramics) are used, and may lead to deterioration in engine performance. Copyright © 2004 John Wiley & Sons, Ltd.