Search Results

Focusing on the dual-mode dual-fuel (DMDF) combustion concept, a combined optimization of the piston bowl geometry with the fuel injection strategy was conducted at low, mid, and high loads. By coupling the KIVA-3V code with the enhanced genetic algorithm (GA), a total of 14 parameters including the piston bowl geometric parameters and the injection parameters were optimized with the objective of meeting Euro VI regulations while improving the fuel efficiency. The optimal piston bowl shape coupled with the corresponding injection strategy was summarized and integrated at various loads. Furthermore, the effects of the key geometric parameters were investigated in terms of organizing the in-cylinder flow, influencing the energy distribution, and affecting the emissions. The results indicate that the behavior of the DMDF combustion mode is further enhanced in the aspects of improving the fuel economy and controlling the emissions after the bowl geometry optimization.

Increasingly strict emission regulations and unfavorable economic climate bring severe challenges to the energy conservation of marine low-speed engine. Besides traditional methods, the energy and exergy analysis could acknowledge the losses of fuel from a global perspective to further improve the engine efficiency. Therefore, the energy and exergy analysis is conducted for a marine low-speed engine based on the experimental data. Energy analysis shows the exhaust gas occupies the largest proportion of all fuel energy waste, and it rises with the increment of engine load. The heat transfer consumes the second largest proportion, while it is negatively correlated to engine load. The energy analysis indicates that the most effective way to improve the engine efficiency is to reduce the energy wasted by exhaust gas and heat transfer. However, the latter exergy analysis demonstrates that there are other effective approaches to improve the engine efficiency.

Owing to the small size of engines and high injection pressures, it is difficult to avoid the fuel spray impingement on the combustion cylinder wall and piston head in Direct Injection Spark Ignition (DISI) engine, which is a possible source of hydrocarbons and soot emission. As a result, the droplets size and distribution are significantly important to evaluate the atomization and predict the impingement behaviors, such as stick, spread or splash. However, the microscopic behaviors of droplets are seldom reported due to the high density of small droplets, especially under high pressure conditions. In order to solve this problem, a “spray slicer” was designed to cut the spray before impingement as a sheet one to observe the droplets clearly. The experiment was performed in a constant volume chamber under non-evaporation condition, and a mini-sac injector with single hole was used.

Controllability of ignition timing and combustion phase by means of dual-fuel direct injection strategy in jet-controlled compression ignition mode were investigated in a light-duty prototype diesel engine. Blended fuel with lower reactivity was delivered in the early period of compression stroke to form the premixed charge, while diesel fuel which has higher reactivity was injected near TDC to trigger the ignition. The effects of several important injection parameters including pre-injection timing, jet-injection timing, pre- injection pressure and ratio of pre-injection in the total heat value of injected fuel were discussed. Numerical Simulation by using CFD software was also conducted under similar operating conditions. The experimental results indicate that the jet-injection timing shows robust controllability on the start of combustion under all the engine load conditions.

The potential of diesel/gasoline RCCI combustion coupled with late intake valve closing (LIVC) and double direct injection of diesel for meeting high fuel efficiency with ultra-low emissions was investigated in this study. The study was aiming at high load operation in a heavy-duty diesel engine. Based on the reactivity stratification of RCCI combustion, the employment of double injection of diesel fuel provided concentration stratification of the high-reactivity fuel, which is to further realize effective control of the combustion process. Meanwhile, late intake valve closing (LIVC) strategy is introduced to control the maximum in-cylinder pressure and nitrogen oxides (NOx) emissions.

Acetone-Butanol-Ethanol (ABE) is an intermediate product in the ABE fermentation process for producing bio-butanol. As an additive for diesel, it has been shown to improve spray evaporation, improve fuel atomization, enhance air-fuel mixing, and enhance combustion as a whole. The typical compositions of ABE are in a volumetric ratio of 3:6:1 or 6:3:1. From previous studies done in a constant volume chamber, it was observed that the presence of additional acetone in the blend caused advancement in the combustion phasing, but too much acetone content led to an increase in soot emission during combustion. The objective of this research was to investigate the combustion of these mixtures in a diesel engine. The experiments were conducted in an AVL 5402 single-cylinder diesel engine at different speeds and different loads to study component effects on the various engine conditions. The fuels tested in these experiments were D100, ABE(3:6:1)10, ABE(3:6:1)20, ABE(6:3:1)10, and ABE(6:3:1)20.

Fuel injection and fuel-air mixture formation processes have significant influence on the performance of spark ignition gas engines. In order to study the fuel enrichment injection process in the pre-chamber of a marine gas engine, the flow field in the pre-chamber during the gas fuel injection period was investigated by the particle image velocimetry (PIV) method. An organic glass model of pre-chamber was made for optical measurement. The flow fields in the pre-chamber with four different gas injection angles were analyzed, respectively. The measurement results were qualitatively compared to the CFD calculation results as the verification of the calculation. Based on the comparison of the PIV experiment results, an optimal gas fuel injection angle was chosen. Furthermore, 3D CFD calculation models with the baseline and optimal fuel injection angles of a marine spark ignited natural gas engine were generated to calculate the working process.

The new DI diesel engine combustion system named Double-Layer Diverging Combustion System (DLDCS) results in a better Brake Specific Fuel Consumption (BSFC) and lower exhaust emissions. The previous results of numerical simulation and bench test of a single cylinder DI diesel engine showed that more homogeneous fuel distribution, better BSFC and lower emission level were obtained by employing this combustion system. In this research, further numerical simulation are employed to seek the best injection advance angle and investigate the influence of different volume fraction and type lines of upper layer with AVL Fire.

In this work, large eddy simulation (LES) with a K-equation subgrid turbulent kinetic energy model is implemented into the CFD code KIVA3V to study the features of liquid fuel spray and combustion using gradually varying grid in a constant volume chamber. The characteristic time-scale combustion model (CTC) incorporating a turbulent timescale is adopted to predict the combustion process and the SHELL auto-ignition model is used to predict auto-ignition. Combustion is also simulated using Parallel Detailed Chemistry with Lu's n-heptane reduced mechanism (58 species), which has been added into the KIVA3V-LES code. The computational results are compared with Sandia experimental data for non-reacting and reacting cases. As a result, LES can capture the complex structure of the spray and temperature distribution as well as the trend of ignition delay and flame lift-off length variations. Better results are obtained using the Parallel Detailed Chemistry than the CTC model.

Early injection timing is an effective measure of pre-mixture formation for diesel low-temperature combustion. Three algebraic subgrid models (Smagorinsky model, dynamic Smagorinsky model and WALE model) and one-equation kinetic energy turbulent model using modified TAB breakup model (MTAB model) have been implemented into KIVA3V code to make a detailed large eddy simulation of the atomization and evaporation processes of early injection timing in a constant volume chamber and a Ford high-speed direct-injection diesel engine. The results show that the predictive vapor mass fraction and liquid penetration using LES is in good agreement with the experiment results. In combustion chamber, the sub-grid turbulent kinetic energy and viscosity using LES are less than with the RANS models, and following the increasing time, the sub-grid turbulent kinetic energy and viscosity also increase and are concentrated on the spray area.

A large eddy simulation approach and different breakup models are used to analyze fuel injection and atomization processes in a constant volume combustion bomb. The study is focused on the influences of the subgrid turbulent kinetic energy, especially the source term induced by the fuel spray, on the droplet movement and spray characteristics. Furthermore, the influence of different subgrid scale (SGS) models, including the constant coefficient and dynamic Smagorinsky models, WALE model and the K-equation turbulent energy transport model, on fuel sprays and the turbulent dispersion of droplets are examined. Factors affecting the fuel spray are discussed based on numerical computations for various operating conditions and are compared with experimental data.

Working process of diesel engine refers to airflow, turbocharger, fuel injection, combustion, heat transfer and chemical reaction powers etc. Hence, it influences power output, fuel consumption, combustion noise and emissions, moreover directly influences reliability and durability of diesel engine. The working process of 6106 diesel engine is simulated by large universal internal combustion engine working process numerical simulation software GT-Power in this paper, and the effects of compression ratio, fuel supply advance angle and valve timing system on performance of diesel engine are analyzed. When valve-timing system is studied, the influence of intake valve close timing, exhaust valve open timing and valve overlap angle on performance are analyzed. On different operating conditions, the different timing of intake close and exhaust open, valve overlap were computed and analyzed. Finally, at different engine conditions, various optimum results were obtained.

To understand the working mechanism of the porous medium (PM) internal combustion engine, effects of a porous medium heat regenerator inserted into a combustion chamber on the turbulent flow field and fuel-air mixture formation are studied by numerical simulation. The cylindrical chamber has a constant volume, in which a disk-shaped PM insert is fixed. A simplified model for the random structure of the PM is presented, in which the PM is represented by an assembly of a great number of randomly distributed solid units. To simulate flows in the PM a Brinkman-Forchheimer-extended Darcy's equation is introduced into the numerical solver. A version of two-equation k - ε turbulence model suggested by Antohe and Lage is employed for the turbulence prediction in the PM. A spray model, in which the effects of drop breakup, collision and coalescence are taken into account, is introduced to describe spray/wall interactions.

The starting knock of R4102 D.I. diesel engine are analyzed experimentally based on the transient speed and first and third cylinder indicator diagrams that were taken from updated data acquisition system developed by the authors[1][2]. The influence of the starting knock on the strength of connecting rod, piston and piston ring are also studied. The results show that the influence of the starting knock is larger than the influence of the rated conditions. So the starting knock must be thought in the engine design.

A new concept of “synthetic performance coefficient of inlet port” in D.I. diesel engines has been proposed from a viewpoint of efficiency of energy conversion in this paper. It makes the performance of various kinds of inlet ports in D.I. diesel engines compared with each other. Based on the regression analysis of the experimental results, it is found that the synthetic performance coefficient of inlet port has a close linear relation to the engine performance, and it can be used as a criterion to optimize the design of inlet port in D.I. diesel engines.

This paper mainly deals with the harmful emission control problem of the diesel engine. Many research works have been carried out on the catalytic conversion of diesel emissions. First, a few kinds of catalyst are prepared, selected by Thermogravimetric Analysis (TGA) and Differential Thermal Analysis (DTA). Three types of catalytic converter are developed. Engine bench tests on these converters loaded with selected catalysts are made. Testing contents are: (1) conversion rate of harmful gases; (2) reduction effect of exhaust smoke; (3) resistant performance of converters and their influences on the engine, etc. Finally, through comparison, the effective catalytic converter is installed on a folklift truck for testing and durability examination. Testing results show that the catalytic converter has higher conversion rate on gaseous emissions, especially for CO and NOx. After two months running, the conversion rates basically keep the original level.

This paper inverstigates a new way of conical spray for medium speed D. I. diesel engine, with which three different construction injectors were used. The feature of conical spray and fuel-air mixture formation were observed by means of schlieren photograph technique. The main result is that the cone top angle of conical injector has influence on formation of fuel-air mixture and performance of engine. The results of test on a single-cylinder engine show the premixed combustion phase was possessed of a large proportions of the whole combustion period, which was become a leading feature. The increasing interest in study of diesel engine combustion is caused by achieving even more stringent emission standards and greatly improving the fuel economy. From present status of this research the traditional combustion system which with orifice nozzel has already exposed some inherent drawbacks.

Taking a specific diesel engine as a calculation example, three kinds of ptimized calculation methods are studied in detail for the optimization of the performance of Diesel Engine cycle and the following conclusions are drawn: Sequential Linear Programming (S.L.P) suits for the rough optimized calculation of the performance of Diesel Engine cycle. Sequential Unconstrained Minimization Technique (S.U.M.T) suits for the precise optimized calculation of the performance of Diesel Engine cycle with less variables. Orthognal Network Optimization Method (O.N.O.M) has a wide adaptability, but calculating time is longer, it suits for the precise optimized calculation of the performance of Diesel Engine cycle with more variables.

A solution for cylinder wall scuffing is researched. By means of the finite element method, a mathematical model to investigate the temperature field and thermal deformation of the piston is established, which can be used for predicting the cylinder wall scuffing in both the design process of a new diesel engine and the improvement process of the combustion system of an operating diesel engine. The experimental data support the calculated results obtained by using the model. As an application example, the temperature fields and thermal deformations of the piston in the 6E150C diesel engine, which suffers from the cylinder wall scuffing during the period of operation, are analyzed quantitatively by using the mathematical model. After an improved piston with new structure and good cooling system is used in the 6E150C diesel engine, the cylinder wall scuffing no longer occurs.

This paper investigates the difference between the traditional diffusion combustion and hot premix film type combustion on improvement of compression ignition engine performance in all respects. The first part of this paper mainly describes the heat release, air fuel mixing, swirl flow and squish flow and also film formation on diffusion combustion. The second part of this paper describes the development of hot premix combustion, its feasibility and guiding principles. The main purpose of this part is to demonstrate three main measures which should be taken in carrying out premix film formation combustion. The first means is air flow guide ring. The second is film formation process and the third is fine particles fuel injectors: one is supermultiple holes injector and the second is conical spray fuel injector.