Investigation of fuel injection rate identification algorithm based on rail pressure fluctuation characteristics induced by injection

As an important part of the common-rail (CR) fuel system for diesel engines, the injector circulation capacity and the fuel injection mass flow rate vary with carbon deposition and wear, affecting the engine output performance. This study proposes a method to identify the fuel injection rate online, based on the rail pressure fluctuation characteristics induced by fuel injection. The control algorithm uses the signal from the existing rail pressure sensor; the diesel engine does not require modification or additional sensors. A quasi-dimensional model of the CR fuel system was built to analyse the rail pressure wave fluctuation characteristics, and a parameter K was defined as the pressure drop rate. Based on K, a control algorithm was proposed. A high-pressure fuel pump test rig was built to test the fuel injection performance under different operating conditions, and the experimental data were processed by wavelet transform. From the test data, the K of the CR system was analysed using the feedback of the rail pressure sensor. The experimental results show that the value of K increases with an increase in the initial pressure and injection pulse, and is independent of the injection mode. The algorithm is feasible, and works more accurately with a longer injection pulse and a lower pump speed. This method uses the existing rail pressure sensor, does not incur extra cost and has great potential for improving the injection accuracy.

Experimental study on the performance of ultra high pressure common rail system

In order to overcome the difficulties of high pressure source design and parts integration in the injector, realizing the ultra high pressure injection and controllable fuel injection rate, an ultra high pressure common rail system based on domestic basic materials and manufacturing technology level was proposed and designed. The working principle of this system was first introduced; the performance test bench of ultra high pressure common rail system was built. Then, the influence of pressure-amplifier device structure parameters on the pressurization pressure peak was analyzed quantitatively, and on the basis of selecting the most appropriate combination of parameters, the pressure and fuel injection rate control characteristics were conducted. The results show that ultra high pressure common rail system can magnify fuel pressure to ultra high pressure state (more than 200 MPa) and by changing the control signal timing of pressure-amplifier device and injector solenoid valve, the flexible and controllable fuel injection rate can be achieved. Under the condition of the same pressurization ratio, the peak value of pressurization pressure increases gradually, and with the increase of pressurization ratio, the increasing trend of the pressurization pressure peak value is nonlinear. At the same time, under the same condition of spring preload, the greater of the spring stiffness, the higher of the rail base pressure can bear, that means the pressure-amplifier device can achieve pressurization at a higher base pressure. But if the spring stiffness is too large, the solenoid valve of pressure-amplifier device will not be opened due to insufficient electromagnetic force, so the specific selection should be considered in a compromise.

A calculation method and experiment study of high-pressure common rail injection rate with solenoid injectors

The high-pressure common rail system has been widely used owing to its precise control of fuel injection rate profile, which plays a decisive role in cylinder combustion, atomization, and emission. The fuel injection rate profile of high-pressure common rail system was studied, and a fuel injection rate profile calculation model is proposed. The model treats the injector as a black box. Some measured data are needed to calculate the parameters in the model. The rise and fall of injection rate is regarded as trigonometric function to reduce the complexity and increase the accuracy. The model was verified using two different types of fuel injectors. The model calculation results were evaluated under various data input conditions. The results show that the model has good applicability to different input data and injectors. In addition, because the model building requires a large amount of experimental data, a comprehensive analysis of various input data was also conducted. The injection profile was analyzed from a new perspective and the regularity of injection rate profile was established.

An Analysis on the Effects of the Fuel Injection Rate Shape of the Diesel Spray Mixing Process Using a Numerical Simulation

In diesel engines, fuel mixing is an important process in determining the combustion efficiency and emissions level. One of the measures used to achieve fuel mixing is controlling the nature and behavior of the fuel spray by shaping the injection rate. The mechanism underlying the behavior of the spray with varying injection rates before the start of combustion is not fully understood. Therefore, in this research, the fuel injection rate shape is investigated to assess the spraying and mixing behavior. Diesel sprays with different ambient temperatures and injection pressures are modeled using the CONVERGE-CFD software. The validation is performed based on experimental data from an Engine Combustion Network (ECN). The verified models are then used to analyze the characteristics of the diesel spray before and after the end-of-injection (EOI) with four fuel injection rate shapes, including a rectangular injection rate shape (RECT), a quick increase gradual decrease injection rate shape (QIGD), a gradual increase gradual decrease injection rate shape (GIGD), and a gradual increase quick decrease injection rate shape (GIQD). The spray vapor penetrations, liquid lengths, evaporation ratios, Sauter mean diameter (SMDs), distributions of turbulence kinetic energy, temperatures, and equivalence ratios were compared under different injection rate shapes. The results show that the QIGD injection rate shape can enhance mixing during injection, while the GIQD injection rate shape can achieve better mixing after the EOI.

A Study of Combustion Characteristics of Two Gasoline–Biodiesel Mixtures on RCEM Using Various Fuel Injection Pressures

Experimental research was conducted on a rapid compression and expansion machine (RCEM) that has characteristics similar to a gasoline compression ignition (GCI) engine, using two gasoline–biodiesel (GB) blends—10% and 20% volume—with fuel injection pressures varying from 800 to 1400 bar. Biodiesel content lower than GB10 will result in misfires at fuel injection pressures of 800 bar and 1000 bar due to long ignition delays; this is why GB10 was the lowest biodiesel blend used in this experiment. The engine compression ratio was set at 16, with 1000 µs of injection duration and 12.5 degree before top dead center (BTDC). The results show that the GB20 had a shorter ignition delay than the GB10, and that increasing the injection pressure expedited the autoignition. The rate of heat release for both fuel mixes increased with increasing fuel injection pressure, although there was a degradation of heat release rate for the GB20 at the 1400-bar fuel injection rate due to retarded in-cylinder peak pressure at 0.24 degree BTDC. As the ignition delay decreased, the brake thermal efficiency (BTE) decreased and the fuel consumption increased due to the lack of air–fuel mixture homogeneity caused by the short ignition delay. At the fuel injection rate of 800 bar, the GB10 showed the worst efficiency due to the late start of combustion at 3.5 degree after top dead center (ATDC).

Fuel Injector Testing Through Development of a New Test Rig

A modified version of fuel injector with higher injection capacity has been developed. To achieve this, the injector plunger diameter is increased to 11mm from current 9.5mm. A new test rig is developed to understand the functioning of the injector due to the changes incorporated. The new test rig is designed to test injector operation without burning the fuel. Since internal combustion is not present an external arrangement is required to run the engine. This is achieved through a 3-phase induction motor, which is coupled with the crankshaft of the engine. The injected fuel is collected form the cylinders and it is then recirculated. A fuel cooling circuit is also incorporated along with the fuel recirculation system to maintain the temperature of fuel at inlet of fuel pump. An oil heating system is installed in the test rig to maintain the viscosity of the oil by heating it. The required systems for driving the engine, fuel cooling and oil heating are implemented as per the design. The test is conducted on a 19 L diesel engine. Parts which are not required for this test like piston, piston rings, intake and exhaust manifold etc are removed from the engine. And the cylinder liner is blocked from below using a plate to facilitate the collection of injected fuel. Engine is made to run using the motoring rig at the rated speed of 1500 rpm for a duration of 250 hours. Instrumented push tubes are used to measure the push tube load. Push tube load is observed to be in the range of 2700 to 3100 lbf, which is high as compared to the earlier model of the injector. Fuel injection rate is obtained from the fuel collected from the cylinders. And the average fuel injection rate is observed as 0.116 to 2.35 kg/min. Thus, the increase in plunger diameter has led to an increase in fuel injection rate