High-pressure Common-rail Injection System Research Articles

Study of the Optimization of Rail Pressure Characteristics in the High-Pressure Common Rail Injection System for Diesel Engines Based on the Response Surface Methodology

This paper establishes a mathematical model of the high-pressure common rail injection system used in diesel engines according to the parameters of its key components, and AMESim 2020 software was used to establish a simulation model of the common rail injection system used in diesel engines. The simulation model mainly includes a high-pressure oil pump model, a common rail pipe model, and a model of four injectors. This paper also describes an experimental analysis of the accuracy of the established simulation model. Through a simulation analysis of the system rail’s pressure fluctuation and pressure characteristics, it was concluded that the length of the common rail pipe, the diameter of the common rail pipe, and the inner diameter of the high-pressure fuel pipes are important influencing parameters for the rail pressure characteristics of the system. In this study, according to the original common rail pipe and high-pressure fuel pipe model, a response surface methodology was used to optimize and analyze the parameters of the common rail pipe and high-pressure fuel pipes, and the optimal size parameters for the common rail pipe and high-pressure fuel pipes were obtained with the minimum rail pressure fluctuations and the average rail pressure setpoint. After the optimization, the pressure for the common rail pipe of the high-pressure common rail system was increased by 0.82%, the pressure fluctuation was reduced by 21.66%, the injection pressure was increased by 1.15%, the single injection volume was increased by 0.86%, and its fuel injection characteristics were significantly improved.

Effect of Intake Conditions and Nozzle Geometry on Spray Characteristics of Group-Hole Nozzle

The group-hole nozzle concept is proposed to meet the requirement of nozzle hole minimization and reduce the negative impact of poor spatial spray distributions. However, there are limited researches on the effects of intake conditions and nozzle geometry on spray characteristics of the group-hole nozzle. Therefore, in this study, an accurate spray model coupled with the internal cavitating flow was established and computational fluid dynamics (CFD) simulations were done to study the effects of intake conditions and nozzle geometry on spray characteristics of the group-hole nozzle. Experimental data obtained using high-speed digital camera on the high-pressure common rail injection system was used to validate the numerical model. Effects of intake conditions (injection pressure and temperature) and nozzle geometry (orifice entrance curvature radius and nozzle length) on the flow and spray characteristics of the group-hole nozzle were studied numerically. The differences in Sauter mean diameter (SMD), penetration length and fuel evaporation mass between single-hole nozzle and group-hole nozzle under different nozzle geometry were also discussed. It was found that the atomization performance of the group-hole nozzle was better than that of the single-hole nozzle under same intake conditions, and the atomization effect of the short nozzle was better than that of the long nozzle. With increase in the orifice entrance curvature radius, the average velocity and turbulent kinetic energy of the fuel increased, which was conducive to improving the injection rate and flow coefficient of the nozzle. Meanwhile, the penetration length and SMD value rose, while evaporation mass dropped. When the ratio of the orifice entrance curvature radius (R) to the diameter of injection hole (D) was 0.12, the spray characteristics reached a constant state due to elimination of cavitation. Conclusions were made based on these. This study is expected to be a guide for the design of the group-hole nozzle.

Investigation of a method for online measurement of injection rate for a high-pressure common rail diesel engine injector under multiple-injection strategies

As a state-of-the-art injection technology, the high-pressure common rail injection system (HPCRIS) has advantages that include high injection pressure, adjustable injection timing and a flexible injection rate. Nevertheless, the fluctuation of cyclic fuel injection mass (CFIM) in the HPCRIS using a multiple-injection strategy (MIS) reduces the economy of the diesel engine and the stability of vibration and noise control. To realize the precise control of CFIM, the online perception of the injection process is the premise. This paper presents an innovative method for online measurement of injection rate under MIS conditions. According to the evolution characteristics of water hammer pressure oscillation in the fuel system, the rule is that the oscillation form of the water hammer is dependent on the structure of the HPCRIS rather than the injection conditions, and the general applicability of this rule is proved by the hydraulic–electric analog method. Based on this, the method for real-time simulation of the pilot water hammer oscillation wave in the same field is proposed to realize the extraction of the expansion pressure signal components of the main injection. Then, the direct mathematical relationship between the pressure signal and fuel injection rate is established, and the online measurement of fuel injection characteristics under MIS is realized. To improve the robustness of the algorithm a method for real-time calibration of fuel sound velocity is proposed. Finally, when compared with the offline experiment, this method for online measurement of injection rate has relatively high accuracy, the CFIM error is less than 2%, and the goodness of fit of the injection rate curve exceeded 0.91. This measurement method can provide direct feedback to the electronic control unit on the fuel injection system without changing the HPCRIS structure.

Experimental investigations into the effects of string cavitation on diesel nozzle internal flow and near field spray dynamics under different injection control strategies

On the test bench of the high-pressure common rail injection system with a high-speed camera, the visualization experiments of real-size tapered hole nozzle of the diesel engine were performed to obtain needle valve lift, string cavitation in the sac chamber and nozzle hole, residual bubbles and near-field spray characteristic. And a high-pressure sensor was utilized to measure the real pressure fluctuation for the nozzle inlet. On the basis, under different control strategies, the comprehensive effects of needle valve throttling and pressure fluctuation for nozzle inlet on the internal flow and near-field spray characteristic under the multiple injections were studied. Research indicated that the spray cone angle and the spray area ratio in the main injection stage shows a boot-shaped increasing trend of slowness and then abruptness. In the development stage, the spray cone angle fluctuates in a little range (20°-30°); In the saturation phase, the spray cone angle fully develops and the fluctuation is relatively stable (40°-50°). As the throttling position shifts, there is an obvious string cavitation process, and the spray cone angle increases suddenly. In the process of pre-injection and post-injection, needle valve and valve seat throttling and lift instability cause fuel pressure fluctuation in the control chamber and sac, which is the main immediate cause of the fluctuation of low fuel injection quantity. Besides, the interval time between multiple injections, on the one hand, affects the state of residual bubbles in the nozzle before the next injection beginning, on the other hand, it also affects the stability of the inlet pressure at this time. The flow transition in the low-lift zone and the cavitation changing in the high-lift stable zone also cause transformation in the form of pressure fluctuation.

Effect of ultrasonic nanocrystal surface modification on wear mechanisms of thermally-sprayed WC-Co coating

High-pressure common rail injection systems lubricated with low-lubricity fuel may be made more resistant to wear and scuffing with robust coatings. In this study, a WC-Co coating was deposited onto heat-treated SAE 52100 steel substrates using a thermal spray method. The coated substrates were then treated using an ultrasonic nanocrystal surface modification (UNSM). Wear performance of the coating was evaluated by ball-on-disk tribometer lubricated with three different fuels against three different materials. Besides, the changes in surface roughness, hardness, microstructural evolution and critical load resulting from UNSM were systematically investigated. The UNSM controlled the surface roughness and hardness due to the grain size refinement, surface integrity and pore reduction. The application of UNSM exhibited higher wear resistance than the as-sprayed coating. Wear mechanisms were investigated based on the results of surface characterizations, where the abrasion and oxidative wear modes took place.

Modelling and experimental investigation of high – pressure common rail diesel injection system

The high-pressure Common Rail (HPCR) injection system was originally introduced for diesel engines to both reduce pollutant emissions and enhancement of performance. HPCR separates fuel pressurization and injection processes from each other. The high injection pressure generated by the common rail system provides better atomisation and evaporation of fuel spray, resulting in improved air inlet and fuel jet mixing, which is advantageous for lowering soot emission. In this paper, a mathematical common rail injection system model has been presented. A Simulink/Matlab code was developed to execute this simulation. This work does not only seek to validate the presented numerical model but to have more insight for understanding the overall common rail injection system diesel engine performance under different operating conditions. Some simulation results are illustrated to highlight modelling capability.The engine used is an HCCI turbocharged diesel engine, 2776 cc, 4-stroke, and 4-cylinder, water-cooled with overhead valve mechanism. The common rail pressure, fuel consumption, start and duration of each injection through one engine cycle are measured at various engine speed and loads. The measured common rail fuel pressure and consumption are used to validate the simulation results. The findings of the simulation show good consistency with the experimental results. At last, some simulation results, which highlight the modelling capability, are illustrated at certain values of engine speed and load.

Optical study of gasoline substitution ratio and diesel injection strategy effects on dual-fuel combustion

Ever growing population and increased vehicles have resulted in higher atmospheric concentration of the greenhouse gases, such as carbon dioxide and methane, thus increasing our planet’s average temperature leading to irreversible climate changes, which has led to increasingly demanding and stricter legislations on pollutant emission and CO2, as well as fuel economy targets for the automotive industry. As a result, a great deal of efforts and resources has been spent on the research and development of high efficiency and low emission engines for automotive applications in the attempt to reduce greenhouse gas emissions and levels of nitrogen oxides and soot emissions, which affect the air quality. This research has developed strategies to investigate the combustion characteristics, engine performance and exhaust emission of diesel–gasoline dual-fuel operation in a Ricardo Hydra single-cylinder optical engine running at 1200 r/min, equipped with a high-pressure common rail injection system for diesel fuel delivery, and a port fuel injection system, designed and manufactured by the author, for gasoline fuel delivery, in order to allow for dual-fuel operations. In-cylinder pressure measurement is used for calculating all engine parameters, heat release rate and efficiency. In addition to the thermodynamic analysis of the combustion parameters, high-speed imaging of spray and combustion chemiluminescence was used for the optical analysis of the effect of the above-mentioned parameters on auto-ignition and combustion processes. Effects of different substitution ratios and diesel injection strategies at low engine loads were studied when the total fuel energy was kept constant. The three main substitution ratios used in this study include 45%, 60% and 75%, which also indicates the amount of fuel energy from port-injected gasoline, where the rest is provided by the direct injection of diesel. Depending on the testing conditions, such as injection strategy and intake conditions, some dual-fuel operations were able to deliver high efficiency and improved emissions compared to that of a pure diesel engine operation, with the diesel–gasoline operation offering more consistency in improved thermal efficiency. The optical analysis of the combustion illustrates the main difference in the flame propagation, distribution and quality for each substitution percentage, as well as the condition under examination. It was observed that combustions with higher concentration of diesel fuel having more diffusion-like combustion, especially with diesel injection timings closer to the top dead centre, where there is less time for the two fuel and air to properly mix before combustion occurs, resulted in higher temperature and levels of NOx due to the pockets of high diesel concentrations within the combustion chamber, whereas higher concentration of gasoline, especially at earlier diesel injection timings, resulted in more homogeneous fuel mixture and thus lower combustion temperatures. In other words, when the gasoline substitution ratio is lower, optimised start of injection is advanced further, so that richer diesel mixture needs longer ignition delay to have proper combustion timing, and combustion is milder and peak heat release rate is slightly lower due to less local diesel rich mixture area by means of earlier injection timing, and in terms of emissions, lower gasoline substitution ratio, decreases NOx with more homogeneous diesel mixture, and same can be said for total hydrocarbon. Performing the thermodynamics testing with an all metal piston alongside the optical testing allowed for the confirmation of these outcomes. This study not only delivers an insight to the benefits of dual-fuel engine operation, it also represents the benefits of optical engines in providing better understanding of engine operation and ways of improving it.

Numerical Simulation of Pressure Fluctuation in High-pressure Common-rail Fuel Injection System

In the past several years, the global diesel engine technology has made significant breakthroughs. The diesel engine has a good economy and power. In 20 years or so, the number of diesel vehicles will exceed the trend of gasoline engines. Diesel engine technology is also developing towards low pollution, low fuel consumption, and high power. To improve the performance of diesel engines, the key is to improve the conversion rate of internal energy to mechanical energy and combustion degrees. In the fuel injection system of diesel engines, a high-pressure common-rail with a large volume is often added between the plunger high-pressure fuel pump and the injector. Its function is to save fuel from the plunger fuel pump, to suppress the fluctuation of oil pressure, and to output high-pressure fuel by adjusting the characteristic parameters of the injector. Firstly, the physical model and mathematical model have been established, including the plunger pump, the high-pressure common rail, and the injector. After that, we use the modified Euler method to solve ordinary differential equations by MATLAB programming. Finally, the Optimized working strategies of plunger pump to inject diesel oil into high-pressure common rail have been obtained. In this high-pressure common rail system, cam of the plunger pump spin 1225.67 times a minute, and pressure relief valve is opened automatically when the pressure in high-pressure common-rail is over 103 MPa, so that the pressure in high-pressure common-rail is approximately stable at 100 MPa, and the fluctuation is small.

Experimental study of the effect of n-butanol additive on spray characteristics of biodiesel in a high-pressure common-rail injection system

The aim of this study was to investigate the spray characteristics of biodiesel and n-butanol/biodiesel blended fuel. The spray tip penetration and the spray cone angle were tested and analyzed. A constant volume chamber and high-speed camera were used to observe the spray evolution and a common-rail system was employed to change the injection pressure. The results show that the spray tip penetration and the spray cone angle of biodiesel are larger than those of blended fuel in most cases. n-Butanol additive changes the relationship between angle and density ratio to a certain degree. The experimental trend lines support the penetration model proposed by Hiroyasu and Arai in terms of similar proportional relation on time after start of injection, and the empirical equations provide reasonable agreement with the experimental data of the spray tip penetration.

An exploration of utilizing low-pressure diesel injection for natural gas dual-fuel low-temperature combustion

It has been widely reported that natural gas dual-fuel combustion (DFC) can achieve much lower soot emissions in contrast to conventional diesel combustion (CDC). Thus, using low-pressure direct injection (LPDI) systems could be an alternative for current high-pressure common rail injection systems, which would significantly reduce the system cost. The present study aimed at exploring the feasibility of LPDI (low to 200 bar) for natural gas DFC in combination of the advanced low temperature combustion technology. The comparative study between natural gas DFC and CDC were carried out. For natural gas DFC, larger advanced injection timing was used to realize low temperature combustion and achieve long ignition delay in order to counteract the negative impact of relatively poor atomization quality caused by the low injection pressure. At DFC mode, higher CO and THC emissions were observed compared to CDC in the cases without EGR. However, DFC was much less sensitive to EGR rate and injection pressure. Natural gas DFC could break the trade-off between NOx and soot emissions, which could achieve low soot and NOx emissions (lower than Europe VI standard: 0.4 g/kW·h) simultaneously at the 42% EGR rate and the 200 bar injection pressure.

Study on seal performance of injector nozzle in high-pressure common rail injection system

The injector needle valve assembly is a key component of the high-pressure common rail fuel injection system of a diesel engine. The sealing performance of the valve assembly significantly affects the normal operation of the engine, the emissions of which can be typically reduced by increasing the pressure of the fuel injection through the valve. However, increased injection pressure causes deformation of the gap of the needle valve assembly; this affects both the leakage from the needle valve assembly and the normal operation of the diesel engine. Herein, to study the effect of fuel pressure on the needle valve assembly leakage, fluid lubrication and tribology principles were used to analyze the sealing mechanism of the valve assembly in the present study. The film thickness and leakage were then simulated using different fuel pressures. In addition, an experiment was performed to verify the results of the theoretical analysis and simulation. It was found that the leakage rate through the needle valve assembly gradually increased with increasing fuel pressure, although the experimentally determined rates under low-pressure conditions were lower than those determined by theoretical analysis and simulation. The results of this study provide a basis for improving the sealing performance and structural optimization of needle valve assemblies.

Experimental Research on the Injection Rate of DME and Diesel Fuel in Common Rail Injection System by Using Bosch and Zeuch Methods

This study investigates a preliminary injection characterization of the injection rate and the injection quantity behavior in a high-pressure common rail injection system used in a heavy-duty engine. The injection rate meter and the injection quantity meter used in the test meter measuring systems were jointly connected under the Zeuch method measurement principles at a constant volume chamber and under the Bosch method measurement principles at a long pipe flow. The trade-off trend for the injection rate and the injection quantity was observed according to the injection pressure. As expected, fuel injection with pilot injection affected the spray quantity and the injection evolution of subsequent fuel injection without pilot injection in dimethyl ether and diesel fuel. The pressure variations in the initial injection duration (2000–6000 µs) of the main and pilot injections for diesel and DME were similar. However, after 7000 µs, the pressure of DME increased more rapidly compared to that of diesel. This finding was the result of the rapid density changes caused by the nature of compressive fluid. Therefore, the DME supply pump was expected to require a higher drive energy by approximately 20% compared to that of the diesel supply pump.

A Study of Spill Control Characteristics of JP-8 and Conventional Diesel Fuel with a Common Rail Direct Injection System

Diversification of energy sources is a key task for decreasing environmental impacts and global emission of gases. JP-8, a fuel derived from natural gas, coal, biomass, and waste plastics, is a bright prospect. JP-8 is considered a multi-source multi-purpose fuel, with several applications. A preliminary characterization of the JP-8 injection rate and injection quantity behavior was investigated based on the high-pressure common rail injection system used in a heavy-duty engine. According to the spill injection and injection pressure, a trade-off trend between injection rate and injection quantity was observed. As expected, pilot injection of JP-8 aviation fuel and diesel fuel affects the spray quantity and injection evolution of the subsequent operation without pilot injection. The difference in spilling between diesel and JP-8 aviation fuel is greater than the difference in injection amount per time; in the process of controlling the injector solenoid through ECU (Electric Control Units), the oil pressure valve and the needle valve operate to a higher extent in order to maintain the diesel fuel’s injection quantity volume. It was found that the total injection quantity was decreased by adding 20% pilot injection duration. Because the pilot injection quantity causes solenoid response, loss and needle lift stroke friction loss.

Experimental and Theoretical Analysis of the Spray Characteristics of a High-Pressure Common-Rail Injection System Fueled with Neat Biodiesel, Ethanol-Biodiesel Blends, and Neat Diesel Fuel

AbstractIn this study, the spray and atomization characteristics of neat biodiesel, ethanol-biodiesel blends (BDEs), and neat diesel in a high-pressure common-rail injection system were investigate...

Reductions in diesel emissions including PM and PN emissions with diesel-biodiesel blends

The current work is an experimental investigation to examine the influence of biodiesel derived from waste cooking oil on engine performance and exhaust emissions. Experiments were conducted with three biodiesel blends at 20%, 40%, and 60% (by volume). A petroleum diesel fuel was used as a reference fuel. The primary purpose of this study was to observe both particulate matter (PM) and particle number (PN) emissions for the three biodiesel blends. Furthermore, the blow-by emissions of the biodiesel blends were also studied. All measurements were conducted in a six-cylinder turbocharged diesel engine with a high-pressure common rail injection system in compliance with a 13-Mode European Stationary Cycle (ESC).

Effects of injection pressure on ignition and combustion characteristics of diesel in a premixed methanol/air mixture atmosphere in a constant volume combustion chamber

The experiments on the ignition and combustion characteristics of diesel in air atmosphere (AA) and premixed methanol/air mixture atmosphere (MAA) were conducted in a constant volume combustion chamber (CVCC) equipped with a high pressure common-rail injection system. The ignition and combustion processes were recorded by a high-speed camera and a combustion pressure acquisition system. Results show that with the increase of injection pressure from 40 to 160MPa, the flame lift-off length (FLoL) becomes longer; and the ignition delay is shortened from 2.80ms to 2.03ms (AA) and 2.90ms to 2.27ms (MAA) respectively; and correspondingly the combustion duration is shortened from 5.17ms to 2.47ms (AA) and 4.83ms to 2.13ms (MAA). Compared those in AA, the ignition delay is prolonged by 0.14ms on average, while the combustion duration is shortened by 0.27ms in MAA. At high injection pressure, the moments that the maximum combustion pressure occurs and the apparent heat release rates (AHRR) starts to rise are advanced; while in MAA both of them are delayed; and the peak value of AHRR increases. With the increase of injection pressure, both spatially integrated natural luminosity (SINL) and time integrated natural luminosity (TINL) reduce significantly, but the reduction trends of TINL weaken. Due to the addition of methanol, the FLoL of diesel becomes longer, and the SINL and TINL in MAA are both lower than those in AA.

Experimental study on spray characteristics of ethanol-aviation kerosene blended fuel with a high-pressure common rail injection system

Partial replacement of fossil fuels by biomass based alternative fuels is considered as a possible option toward sustainability in aviation applications. The present work aims to study the changes in the spray characteristics in a pressure vessel when operated with aviation kerosene and ethanol-aviation kerosene blended fuel in a high-pressure common rail injection system. This research proposes the concept of adding a certain percentage of ethanol to aviation kerosene, creating ethanol-aviation kerosene blended fuel, which can decrease our reliance on fossil fuels on some level. The spray characteristics of the blended fuel, like spray tip penetration, spray cone angle and spray area, are studied in our work. Through the analysis, we can find that the atomization conditions have a significant impact on the spray characteristics of the aviation kerosene. Similarly, the experimental results show that the addition of ethanol has certain effect on the spray characteristics of the aviation kerosene. And the empirical equations applied in this study to predicting spray tip penetration and spray tip velocity provide a good agreement with the experimental data in the error-allowed range.

Effect of di-n-butyl ether blending with soybean-biodiesel on the near-nozzle spray characteristics

In this work, the near-nozzle spray characteristics of soybean biodiesel, di-n-butyl ether (DBE)/biodiesel blends and 0# diesel were investigated by using a high pressure common-rail injection system and the effect of experiment conditions and fuel physical properties on the near-nozzle spray structures were explored. Microscopic spray images at the near-nozzle field were captured by the high-resolution microscopy. The micro spray cone angle and micro projected spray area were obtained from the processed spray images for quantitative analysis. The results show that the initial spray of diesel is easier to breakup into ligaments and droplets because of smaller surface tension and viscosity compared to that of biodiesel under atmospheric condition. The spray with more ligaments was easily restrained by the ambient gas and promoted to evolve along the radial direction, leading to a wider micro spray cone angle of diesel. The breakup of liquid jet also tends to increase the micro projected spray area of diesel. When 30% of DBE was added into biodiesel, both the micro spray cone angle and projected spray area were increased due to the decreased surface tension and viscosity of the blended fuel. The initial spray images reveal that the high injection pressure favors the spray primary breakup while the high ambient pressure results in worse spray primary breakup. The quantitative analysis shows that the injection pressure has little influence on the micro spray cone angle but results in the increase in micro projected spray area, while both parameters increase significantly under high ambient pressures.

Experimental investigation on the effect of n-butanol blending on spray characteristics of soybean biodiesel in a common-rail fuel injection system

In this work, the spray and atomization characteristics of neat soybean biodiesel fuel (BD100) and biodiesel/n-butanol blends (BDB80, 20% of n-butanol (wt.)), were investigated at room temperature and ambient pressure of 1 and 2MPa. A high-pressure common-rail injection system was used to generate sprays from an injector (aperture 0.25mm) at a maximum injection pressure of 100MPa. High speed schlieren technique was used to record the highly transient spray penetration process, through which the spray macroscopic parameters such as spray tip penetration, spray cone angle, projected spray area and spray volume were deduced. In addition, droplet size, number density and its sauter mean values at specific location within the spray cone was analyzed, by using a particle/droplet image analyzing technique (PDIA). Results show that longer spray tip penetration and larger droplet diameters were observed for BD100, compared with BDB80, which was attributed to the lower viscosity and surface tension of BDB80. BDB80 has a spray volume less than BD100, the same trend is also observed in the spray tip penetration. BD100 presents bigger spray area than BDB80 under 1MPa ambient pressure. This is mainly attributed to the bigger spray tip penetration of BD100. The results also show that droplets at the spray periphery have larger diameters than those in the center of the spray due to the effect of air entrainment at the spray periphery. The small particles of fuels are easily sucked into internal of spray. Furthermore, the droplets near the liquid core of spray have more small numbers, where the effect of viscosity is dominant.

High pressure common rail injection system modeling and control

In this paper modeling and common-rail pressure control of high pressure common rail injection system (HPCRIS) is presented. The proposed mathematical model of high pressure common rail injection system which contains three sub-systems: high pressure pump sub-model, common rail sub-model and injector sub-model is a relative complicated nonlinear system. The mathematical model is validated by the software Matlab and a virtual detailed simulation environment. For the considered HPCRIS, an effective model free controller which is called Extended State Observer – based intelligent Proportional Integral (ESO-based iPI) controller is designed. And this proposed method is composed mainly of the referred ESO observer, and a time delay estimation based iPI controller. Finally, to demonstrate the performances of the proposed controller, the proposed ESO-based iPI controller is compared with a conventional PID controller and ADRC.