Search Results

TWC exposure to extreme temperature could result in irreversible damage or thermal failure. Thus, a strategy embedded in the engine control unit (ECU) called catalyst overheating protection (COP) will be activated to prevent TWC overheating. When COP is activated, the command air-fuel ratio will be enriched to cool the catalyst monolith down. Fuel enrichment has been proven a main prerequisite for ammonia formation in hot TWCs as a by-product of NOx reduction. Hence, COP events could theoretically be a source of post-catalyst ammonia from petrol vehicles, but this theory is yet to be confirmed in published literature. This paper validated this hypothesis using a self-programmed chassis-level test. The speed of the test vehicle was set to constant while the TWC temperature was raised stepwise until a COP event was activated.

In this paper, a new method for the driving of the hydraulic free piston engine (HFPE) is proposed. Hydraulic differential drive achieves the compression stroke automatically rather than special recovery system, which has a great influence on the engine dynamic performance. The purpose of this paper is to solve the key operation and control problems for HFPE to commix fuel with air. HFPE adopts two-stroke loop-scavenging and semi-direct injection. The semi-direct injection nozzle is located in the liner wall inside the main intake port, with the axes oriented towards the piston at the Bottom Dead Center (BDC). Different scavenging pressures and injection angles result in different impacts on the mixture of fuel and air in the cylinder. This study analyzes the changes of the combustion heat release rate by simulation.

Urea SCR technology is the most promising technique to reduce NOx emissions from heavy duty diesel engines. 32.5wt% aqueous urea solution is widely used as ammonia storage species for the urea SCR process. The thermolysis and hydrolysis of urea produces reducing agent ammonia and reduces NOx emissions to nitrogen and water. However, the application of urea SCR technology has many challenges at low temperature conditions, such as deposits formation in the exhaust pipe, lack deNOx performance at low temperature and freezing below -12°C. For preventing deposits formation, aqueous urea solution is hardly injected into exhaust gas stream at temperature below 200°C. The aqueous urea solution used as reducing agent precursor is the main obstacle for achieving high deNOx performances at low temperature conditions. This paper presents a solid SCR technology for control NOx emissions from heavy duty diesel engines.

This paper describes the application of Human Simulation Intelligent Control(HSIC) method to improve the idle speed performance of heavy-duty diesel engines on the basis of diesel engine electronic control system. The HSIC is a kind of intelligent control method which can be used without knowing the system's model and it can on line choose control models and it is also easy to be used under the condition of diesel engine electronic control system. In our system, we used electronic control system to control fuel quantity by double loop control of pump rack position and engine speed. From the experimental results, The engine minimum idle speed has been reduced from 800 rpm at first to 500 rpm, and the speed fluctuation have been reduced by 50 percent. From the system's design and test, the simplicity and efficiency of the HSIC control method were demonstrated.

Radial flow Variable Nozzle Turbine (VNT) enables better matching between the turbocharger and engine. At partial loading or low-end engine operating points, the nozzle vane opening of the VNT is decreased to achieve higher turbine efficiency and transient response, which is a benefit for engine fuel consumption and emission. However, under certain small nozzle opening conditions (such as nozzle brake and low-end operating points), strong shock waves and strong nozzle clearance flow are generated. Consequently, strong rotor-stator interaction between turbine nozzle and impeller is the key factor of the impeller high cycle fatigue and failure. In present paper, flow visualization experiment is carried out on a linear turbine nozzle. The turbine nozzle is designed to have single-sided clearance, and the Schlieren visualization method is used to describe the formation and development process of clearance flow and shock wave under different clearance and expansion ratio configurations.

The electric compound turbocharger(ECT) which integrates a high speed motor into a turbocharger rotor shaft can be used transiently to accelerate the turbocharger more quickly in response to an acceleration requirement. It can utilize the exhaust gas energy fully to improve the engine fuel efficiency and benefit for engine with lower emissions. The key technique of ECT is to solve the reliability problems when an electrical motor is integrated into a turbocharger shaft between the turbine and compressor wheels will increase the burden for the bearing support and affect the turbocharger shaft rotation characteristics. In order to know the dynamics behavior of higher load bearing system is explored for reliability, this paper focus on the nonlinear rotor dynamics characteristics of ECT rotor bearing system.

The spray structure and vaporization processes of flash-boiling sprays in a constant volume chamber under a wide range of superheated conditions were experimentally investigated by a high speed imaging technique. The Engine Combustion Network’s Spray G injector was used. Four fuels including gasoline, ethanol, and gasoline-ethanol blends E30 and E50 were investigated. Spray penetration length and spray width were correlated to the degree of the superheated degree, which is the ratio of the ambient pressure to saturated vapor pressure (pa/ps). It is found that parameter pa/ps is critical in describing the spray transformation under flash-boiling conditions. Three distinct stages namely the slight flash-boiling, the transition flash-boiling, and the flare flash-boiling are identified to describe the transformation of spray structures.

The hydraulic free piston engine is a complex mechanical-electro-liquid system, in order to simplify the complex system of the single hydraulic free piston engine, a new method for the driving of hydraulic free piston engine is proposed. Hydraulic differential drive achieves the compression stroke automatically rather than special recovery system. The structure and principle of hydraulic differential drive free-piston engine are analyzed and the mathematical model is established based on the piston force analysis and the hydraulic system working principle. In addition, the control strategy of this novel hydraulic driving engine is also introduced. Finally, the transient results of dynamics are obtained through simulation. Then we compare our results to the ones from the hydraulic free piston engine made by the company Innas.

In this paper, a new-type balanced opposed-piston two-stroke (OP2S) gasoline direct injection (GDI) engine is developed by Beijing Institute of Technology. OP2S-GDI engine has some potential advantages such as simple structure, good balance, compact, high power density and thermal efficiency. The structural feature of OP2S-GDI engine leads to the performance difference compared with conventional engines. In order to study and verify the characteristics of this kind of engine, the dynamics characteristics and design scheme of opposed crank-connecting rod mechanism, in-cylinder scavenging process, mixture formation and combustion process are investigated. The influence of parameters on engine performance is investigated, including opposed-piston motion phase difference, intake and exhaust port timing, injection and ignition timing.

The method and steps for software modeling of the embedded control systems for diesel engine based on UML are described in this paper. In order to meet the software function and the features of the system, object-oriented modeling for diesel engine embedded control software system has been implemented. Requirements are depicted by use case diagram and the logic structure is depicted by class diagram. According to the domain knowledge and the class diagram, the sequence diagram and state diagram are developed to describe the dynamic behavior of the system. The level of software development has been enhanced to the system level by software modeling. It focuses on the automotive field, and can be easy to grasp the problem from the overall perspective and discover software design problems at the early stage. It is also convenient to solve the problems caused by the change of requirements. The model has an excellent flexibility so that it can be applied to different software platforms.

The cylinder-by-cylinder variations have many bad impacts on the engine performance, such as increasing the engine speed fluctuation, enlarging the torsional vibration and noise. To deal with this problem, the impact mechanism of cylinder-by-cylinder variations on low order torsional vibration has been studied in this paper, and subsequently a new individual cylinder control strategy was designed by processing the instantaneous crankshaft rotation speed signal, detecting the cylinder-by-cylinder variation and using feed-back control. The acceleration characteristics of each cylinder in each engine cycle were compared with each other to extract the variation index. The feed-back control algorithm was based on the regulation of the fuel injection according to the detected variation level.

The principal objective of the present work is to investigate the fundamental characteristics of a commercially available outwardly opening twin-fluid injector, which utilizes air-assisted atomization principle to attain pulse-type injection of fuel-air mixture. The electromagnetic characteristics of this injector were simulated and the effects of dominating parameters on the electromagnetic force to drive injector were ascertained. On that basis, this paper elaborates on the fundamental characteristics of air-assisted spray using gasoline and kerosene with the employment of two types of optical testing techniques. The spray morphological evolution under varied fuel injection durations and ambient pressures were captured with high-speed shadowgraph thus the corresponding external macroscopic characteristics were obtained and further compared. Spray droplet velocity and diameter at fixed monitoring location were measured by using PDPA (Phase Doppler Particle Analyzer).

The Opposed Piston Two-Stroke (OPTS) engine has many advantages on power density, fuel tolerance, fuel flexibility and package space. A type of self-balanced opposed-piston folded-crank train two-stroke engine for Unmanned Aerial Vehicle (UAV) was studied in this paper. AVL BOOST was used for the thermodynamic simulation. It was a quasi-steady, filling-and-emptying flow analysis -- no intake or exhaust dynamics were simulated. The results were validated against experimental data. The effects of high altitude environment on engine performance have been investigated. Moreover, the matching between the engine and turbocharger was designed and optimized for different altitude levels. The results indicated that, while the altitude is above 6000m, a multi-stage turbocharged engine system need to be considered and optimized for the UAV.

Based on BF6M1015CP electronic diesel engine (it is a supercharged, water-cooled engine. It has 6 cylinders and it is for heavy-duty vehicle) and HD4070PR electronic automatic transmission (it covers heavy-duty applications requiring high input horsepower and torque. It contains torque converter module, control module, planetary module and output module. It has 7 forward gears and a power-take -off (PTO) and a retarder), the paper analyzes the shift system of an electronic automatic transmission and sets up a mathematic module of the shifting process. With the model the shifting process is analyzed and the model can be used directly in shifting process control, and the rules of shifting process can be derived. To improve the shift quality, in the paper the different control methods in different phases are used and reviewed that Include the open-loop control, fixed ramp rate, and closed-loop control.

Aiming at the high altitude operation problems for piston-type aero-engines and to improve the practical ceiling and high altitude dynamic performance, this thesis analyzes a controllable three-stage composite supercharging system, using a two-stage turbocharger coupled supercharger method. The GT-Power simulation model of a four-cylinder boxer engine was established, and the control strategy of variable flight height was obtained. The simulation research of engine performance from 0 to 20,000 meters above sea level has been carried out, which shows that the engine power is at the same level as the plain condition, and it could still maintain 85.28 percent of power even at the height of 20,000 meters, which meets the flight requirements of the aircraft.

The output power of a turbocharged diesel engine will decrease and the maximum torque point in the full load torque map will move backwards when the engine is operating at plateau.

One-dimensional combustion performance of a turbocharged V-type eight-cylinder diesel engine was computed by used of WAVE code. The parameters of compress ratio, intake temperature, intake pressure, fuel injection quantity, advance angle of injection, fuel injection rate and fuel injection duration were changed so as to study quantificationally how these parameters affect the power, fuel consume, the max combustion pressure, exhaust temperature and emission of the diesel engine. The computational results could help to accomplish the preliminary optimization of several parameters for combustion matching and supplement experimental experience and exploit new products.

For the application of advanced clean combustion technologies, such as diesel HCCI/LTC, a compressor with high efficiency over a broad operation range is required to supply a high amount of EGR with minimum pumping loss. A compressor with high pitch of vaneless diffuser would substantially improve the flow range of the compressor, but it is at the cost of compressor efficiency, especially at low mass flow area where most of the city driving cycles resides. In present study, an ultra low solidity compressor vane diffuser was numerically investigated. It is well known that the flow leaving the impeller is highly distorted, unsteady and turbulent, especially at relative low mass flow rate and near the shroud side of the compressor. A conventional vaned diffuser with high stagger angle could help to improve the performance of the compressor at low end. However, adding diffuser vane to a compressor typically restricts the flow range at high end.

This paper investigates the scavenging process, in-cylinder gas motion in an opposed-piston two-stroke diesel engine and compares the results of in-cylinder gas motion to those of a uniflow-scavenged two stroke conventional engine using computational fluid dynamics engine models. The effect of piston motion profile of OP2S on the scavenging performance was discussed and its optimization was developed. Subsequently, CFD simulation on full load scavenging process was conducted at the same intake pressure and simulation at 2500rpm showed an optimum scavenging performance evaluated by delivery ratio, trapping efficiency and scavenging efficiency. Enhanced axial velocity and average turbulence kinetic energy around minimum volume center were found for OP2S diesel engine compared to the conventional two-stroke diesel engine.

An opposed piston two-stroke engine is more suitable for use in an unmanned aerial vehicle because of its small size, excellent self-balancing, stable operation, and low noise. Consequently, in this study, based on experimental data for a prototype opposed piston two-stroke engine, numerical simulation models were established using GT-POWER for 1D simulation and AVL-FIRE for 3D CFD simulation. The mesh grid and solver parameters for the numerical model of the CFD simulation were determined to guarantee the accuracy of the numerical simulation, before studying and optimizing the ventilation efficiency of the engine with different dip angles. Furthermore, the fuel spray and combustion were analyzed and optimized in details.