Fuel Injection Quantity Research Articles

Investigation of the optimal timing and amount of fuel injection on the efficiency and emissions of a diesel engine through experimentation and numerical analysis

The purpose of this study is to investigate the performance, in-cylinder combustion, and emissions of the MTE660E heavy-duty diesel engine using 3D CFD simulation. The CFD simulation model based on AVL FIRE software was developed to numerically investigate the performance, in-cylinder combustion, and emissions of the MTE660E engine. The AVL model was validated against empirical data. The 6-cylinder MTE660E engine was operated under a constant excess air ratio of 1.75 and at 1600 rpm engine speed. The geometry and lattice design of the MTE660E engine were simulated to provide a computationally efficient approach. The AVL model was validated against experimental data and the error between the measured and calculated value of combustion characteristics and emissions was acceptable (R2> 90 %), error <5.6 %). Design Expert software was used to optimize the dependent variables (peak chamber temperature, brake mean effective pressure, engine torque, engine thermal efficiency and emissions of NOx) according to the studied variables (injection time and fuel injection quantity) based on response surface methodology. The results show that the recommended injecting time of 342 °C and the specific amount of fuel lead to better combustion efficiency, resulting in high engine performance and low emissions. The specific fuel consumption was highest at 2200 rpm with a 50 % load, while the lowest SFC level was observed at 1750 rpm with a 100 % load. The maximum value of NOx emissions was observed at full load. The findings show that the optimization of the injection timing and fuel injection quantity can effectively enhance the performance of the MTE660E engine. The study provides valuable insights into improving combustion efficiency, resulting in greater performance and reduced emissions without requiring expensive overhaul. It has potential applications in automotive and commercial transportation industries, thereby reducing fuel consumption and emissions.

Numerical Study on the Potential of Stratified Mixture to Improve Thermal Efficiency and Reduce Carbon Emissions in High-Speed Gasoline Direct Injection Engine

Abstract Stratified combustion improves the indicated thermal efficiency (ITE) of gasoline direct injection (GDI) engines, but the mechanism of its impact on unregulated emissions remains unclear. In this simulation-based study, double injection strategies were used to create stratified mixtures in the cylinder. The results indicated that as the second fuel injection quantity (FIQ) was increased or as the second fuel injection timing (FIT) was delayed, the oil-film mass increased, leading to an increase in soot emissions. The formation of a large area of stoichiometry (STO) region at the spark plug and at its right side increases the laminar flame velocity and improves the ITE. At 4000 rpm, the ITE of case2-2 (with a second FIT of −220 °CA after top dead center (ATDC) and a second FIQ of 65.5 mg) increased by 1.6% compared to the original scheme. With the increase in STO area, NOx emissions and the content of CH3OH and CH2O increased, while carbon monoxide (CO) and greenhouse gas emissions showed a decreasing trend. Compared to the original scheme, CO and greenhouse gas emissions decreased by 1.97% and 6.7%, respectively, in case2-2. This study provides guidance for the development of GDI engines with high ITE and low carbon emissions.

Study on precise fuel injection under multiple injections of high pressure common rail system based on deep learning

The fluctuation of fuel injection quantity under multiple injections of high pressure common rail system leads to a decline in engine economy and emission performance, the precise injection control is the key problem in current research. In this study, a deep learning data-driven model of injection quantity under multiple injections was established based on generalized regression neural network (GRNN), and the particle swarm optimization (PSO) was introduced to optimize the smoothing factor in the model, thereby improving its prediction accuracy. An injection quantity correction method based on the data-driven model was proposed and applied to actual common rail fuel injection system for experimental verification. The results demonstrate that the proposed data-driven model has excellent prediction performance and generalization ability for the predicted main injection quantity with mean absolute percentage error of 1.10 % and determination coefficient of 0.997. Through the experimental verification of the correction method under 144 groups of operating conditions, it was observed that the maximum deviation of main injection quantity decreased from −25.83～17.91 mm3 to −9.81～7.64 mm3, and the maximum absolute deviation reduced by 62.02 %. The precise of injection control under multiple injections is improved.

Optimizing Fuel Injection Timing for Multiple Injection Using Reinforcement Learning and Functional Mock-up Unit for a Small-bore Diesel Engine

&lt;div&gt;Reinforcement learning (RL) is a computational approach to understanding and automating goal-directed learning and decision-making. The difference from other computational approaches is the emphasis on learning by an agent from direct interaction with its environment to achieve long-term goals [&lt;span&gt;1&lt;/span&gt;]. In this work, the RL algorithm was implemented using Python. This then enables the RL algorithm to make decisions to optimize the output from the system and provide real-time adaptation to changes and their retention for future usage. A diesel engine is a complex system where a RL algorithm can address the NO&lt;sub&gt;x&lt;/sub&gt;–soot emissions trade-off by controlling fuel injection quantity and timing. This study used RL to optimize the fuel injection timing to get a better NO–soot trade-off for a common rail diesel engine. The diesel engine utilizes a pilot–main and a pilot–main–post-fuel injection strategy. Change of fuel injection quantity was not attempted in this study as the main objective was to demonstrate the use of RL algorithms while maintaining a constant indicated mean effective pressure. A change in fuel quantity has a larger influence on the indicated mean effective pressure than a change in fuel injection timing. The focus of this work was to present a novel methodology of using the 3D combustion data from analysis software in the form of a functional mock-up unit (FMU) and showcasing the implementation of a RL algorithm in Python language to interact with the FMU to reduce the NO and soot emissions by suggesting changes to the main injection timing in a pilot–main and pilot–main–post-injection strategy. RL algorithms identified the operating injection strategy, i.e., main injection timing for a pilot–main and pilot–main–post-injection strategy, reducing NO emissions from 38% to 56% and soot emissions from 10% to 90% for a range of fuel injection strategies.&lt;/div&gt;

Effects of fuel injection pressure and quantity on low octane gasoline sprays in a simulated high-pressure ambient environment of a gasoline compression ignition engine

Gasoline Compression Ignition technology using low-octane gasoline-like fuel can lead to very low NOx and Soot emissions and enhanced thermal efficiency than conventional diesel engines. The difference in test fuel properties is a significant reason for the difference in the fuel–air mixture formation in Gasoline Compression Ignition engines offering these advantages. In this study, microscopic and macroscopic spray characterisation of baseline diesel, 50 % v/v diesel blended with 50 % v/v gasoline (G50), and 20 % v/v diesel blended with 80 % v/v gasoline (G80) are conducted in a high-pressure ambient environment relevant to Gasoline Compression Ignition engines. The study was performed in a constant volume spray chamber in non-reacting conditions using Phase Doppler Interferometry and Diffused Backlit Illumination techniques. The test fuels were injected into a 30 bar ambient pressure environment at 400, 500, and 700-bar fuel injection pressures. The liquid spray penetration length of gasoline-diesel blends was slightly shorter than baseline diesel, but their spray cone angles and entrained air mass were significantly higher. The average axial droplet velocity was higher, and the Sauter Mean Diameter was lower for gasoline-diesel blends than baseline diesel 40 mm away from the injector nozzle exit, indicating superior mixture formation for the gasoline-diesel blends. The effect of droplet collision and injected fuel quantity on droplet size distribution was assessed in all test fuels. Droplet collisions increased the Sauter mean diameter of the spray at farther distances. Smaller fuel injection quantities decreased the Sauter mean diameter of the spray, increasing the probability of unburnt hydrocarbon emission producing ultra-lean regions in the engine combustion chamber.

Effective measures to improve thermal efficiency of medium-sized diesel engine in practical application: Energy-exergy analysis and test verification

As the fourth stage of China’s fuel consumption limits for heavy commercial approaches, engine manufacturers are facing huge challenges. Here, the impact of different strategies on brake thermal efficiency (BTE) was studied through experiments and simulations, and the main energy loss items were obtained based on energy and exergy analysis. According to experimental results, the removal of exhaust gas recirculation (EGR) mainly reduced exhaust losses, resulting in a 0.5% increase in BTE at 1200 r/min. Turbocharger scheme 2, with a high flow rate and high efficiency, was beneficial in reducing pumping losses. Owing to consistent brake power, simultaneously increasing the compression ratio and peak firing pressure can reduce the exhaust losses and combustion irreversibility. When fuel injection quantity was constant, the use of high flow injectors could advance CA50, thereby increasing output power and reducing exhaust losses. Finally, the actual development of the new engine was completed, and the test results showed that the maximum BTE reached 46.9%, and CO and soot emissions were reduced by 74.2% and 78.3%, respectively. Therefore, for medium-sized diesel engines, adopting the non-EGR route, using high flow turbochargers and injectors, and increasing compression ratio can effectively improve BTE and reduce carbon emissions.

Effects of a Self-Pressurized Injection Strategy on the Formation of a Stratified Mixture and the Combustion of an Aviation Kerosene Piston Engine

Abstract The aviation kerosene piston engine (AKPE) is the main power system for small- and medium-sized unmanned aerial vehicles (UAVs). Conventional AKPEs use carburetors or port fuel injection (PFI) as fuel supply, resulting in poor cold start performance and difficulty in forming an economically efficient stratified mixture. In addition, two-stroke AKPEs using carburetors or PFI have serious scavenging losses. These reasons lead to the poor economic performance of conventional AKPEs. Direct injection (DI) can be controlled through precise injection timing to form a stratified mixture. The combustion of stratified mixtures in engines can effectively improve the fuel economy and endurance flight time characteristics of UAVs. As a special DI injector, self-pressurized injectors have great potential in the power field of UAVs. To effectively apply self-pressurized injectors on UAV engines and improve the economy, an engine model and a self-pressurized injector spray model are established and verified in this paper. The single injection strategy and segmented injection strategy for forming stratified mixtures are explored, and the combustion performance is studied. The main conclusions are as follows: the optimal installation angle of the injector is 15 deg, which yields excellent results in the formation of the mixture at this angle. When the fuel injection quantity is small, utilizing a single injection strategy combined with delaying the end of the injection phase (EOIP) can form a stratified mixture. Reducing the angle difference between the EOIP and the ignition timing can improve the power and economy. As the fuel injection quantity is large, a stratified mixture can be formed through two-stage injection. When the fuel injection ratio is 4:1, the uniformity of the mixture distribution in the combustion chamber is significantly improved. Adjusting the second EOIP between a 35 deg crank angle (CA) before top dead center (BTDC) and a 30 deg CA BTDC can achieve a stratified mixture with good economy and power performance.

Methanol (M85) Port Fuel-Injected Spark Ignition Motorcycle Engine Development—Part 1: Combustion Optimization for Efficiency Improvement and Emission Reduction

&lt;div&gt;Limited fossil fuel resources and carbonaceous greenhouse gas emissions are two major problems the world faces today. Alternative fuels can effectively power internal combustion engines to address these issues. Methanol can be an alternative to conventional fuels, particularly to displace gasoline in spark ignition engines. The physicochemical properties of methanol are significantly different than baseline gasoline and fuel mixture-aim lambda; hence methanol-fueled engines require modifications in the fuel injection parameters. This study optimized the fuel injection quantity, spark timing, and air–fuel ratio for M85 (85% v/v methanol + 15% v/v gasoline) fueling of a port fuel-injected single-cylinder 500 cc motorcycle test engine. Comparative engine performance, combustion, and emissions analyses were performed for M85 and baseline gasoline. M85-fueled engine exhibited improved combustion characteristics such as higher peak in-cylinder pressure, heat release rate, and cumulative heat release due to higher flame speed and the effect of fuel oxygen. The brake thermal efficiency increased by up to 23% at lower loads and 8% at higher loads for M85 fueling. Carbon monoxide was reduced by 11.4–94% and 46.1–94.4% for M85 w.r.t. baseline gasoline at 2500 and 3500 rpm, respectively, at varying engine loads. Hydrocarbon emissions showed mixed trends for M85 w.r.t. baseline gasoline. Nitric oxide emissions were 4–90.2% higher for M85 w.r.t. baseline gasoline at 2500 rpm, at varying engine loads; however, mixed trends were observed at 1500 and 3500 rpm. Carbon monoxide, hydrocarbons, and nitric oxide emissions were 4.6, 38.9, and 84.3% lower for M85 than baseline gasoline during idling. Overall the M85-fueled motorcycle engine emitted fewer harmful pollutants, indicating its superior environmental sustainability, except for slightly higher NO emission.&lt;/div&gt;

Effect of pilot fuel injection strategies and EGR on a CRDI diesel engine powered by simmondsia chinensis seed biodiesel-methyl acetate blend

The primary goal of this research is to produce energy from discarded Simmondsia chinensis seeds. In a CRDI diesel engine, methyl acetate (MA), a novel and renewable component, is blended with Simmondsia chinensis biodiesel (SCB), and various fuel injection techniques and exhaust gas recirculation (EGR) are employed. After that, the fuel was compared to diesel fuel to improve ignition patterns and reduce exhaust emissions. Non-edible biodiesel has a higher viscosity than diesel, resulting in higher emissions. So, the novel oxygenated additive MA was used as an ignition enhancer. Initially, the test used diesel at 10% EGR and DBMA20 (50% Diesel, 30% SCB + 20% MA by vol.) at 10% EGR. Results found that the brake thermal efficiency (BTE) decreased, and emissions increased. Further, work carried out modified operating parameters pilot injection timing (PIT), pilot fuel injection quantity (PFIQ), and EGR at maximum load conditions. The experiments were done with an optimal blend ratio of DBMA20 at 10% EGR with PIT (35°bTDC, 40°bTDC, and 45°bTDC) and PFIQ (10, 15, and 20% by vol.). The results revealed that at peak load, PIT 45° at PFIQ 20%, the BTE increased by 1.71%, BSFC decreased by 21.87%, SO reduced by 26.61%, HC reduced by 47.69%, CO reduced by 56.41%, and NOx reduced by 11.34 % when contrasted with the DBMA20 outcomes with 10% EGR at standard injection settings. So, the PIT 45° at PFIQ 20% with 10% EGR was better than the other operating conditions. As a result, using biodiesel along with a pilot fuel injection technique was viable in operating conditions to improve efficiency and reduce emissions in CRDI diesel engine applications.

Dynamic Modelling of Common Rail Diesel Engines Combined with Amesim and Simulink

The fuel injector of the diesel engine is the core component of the high-pressure common rail system of the diesel engine. The ECU performs flexible control on the fuel injector to realize the precise adjustment of the fuel injection rate and fuel injection quantity of the engine under different working conditions, and achieve the purpose of reducing fuel consumption and noise. The internal structural parameters of the fuel injector have a significant impact on the fuel injection rate, and it is often necessary to make a large number of modifications to the structural parameters of the fuel injector in order to meet the increasingly stringent emission regulations. In this paper, in order to analyze the effect of various structural parameters of fuel injectors on fuel injection rate, increase fuel injection rate, and obtain the best effect, AMESim and simulink software are used to build a simulation model of a common rail fuel injection device and a diesel engine. This model provides a theoretical basis for the structure design of the fuel injector.

Experimental study on flame combustion characteristics of large-bore marine diesel engine based on endoscopic technology

Large-bore marine diesel engines have the characteristics of poor ignition performance and insufficient combustion in the cylinder. This work revealed the combustion and emission performance of large-bore marine diesel engines based on endoscopic visualization technology. The flame temperature and soot distribution were analyzed in radial and axial directions. Results show that the large-bore diesel engine has a poor combustion effect because of the large fuel injection quantity and insufficient fuel-air mixing effect in the cylinder. The temperature in the cylinder rises twice in the late stage of combustion. The average temperature rises by 3.8%, caused by the secondary ignition of part of the unburned diesel. In addition, the large-bore engine produces a large amount of soot due to an insufficient mixing effect. It can be observed from the radial flame visualization images that the propagation speed of the flame is slow. The time required for the flame to propagate to the wall at 50% load is reduced by 31% compared with 25% load. The downward movement of the piston causes the flame tumble flow in the cylinder, resulting in an apparent asymmetric structure of the flame development.

Experimental observation of turbulent jet ignition of pre-chamber with scavenging system for carbon dioxide diluted mixtures

The exhaust gas recirculation (EGR) method can suppress knock and improve the thermal efficiency of engines. But it will also deteriorate the combustion stability and engine power. Turbulent jet ignition (TJI) is a reliable ignition resource for improving ignition stability and burning rate. However, the residual productions in the pre-chamber will worsen the performance of the TJI. To this end, a self-designed pre-chamber with a scavenging system has been proposed. In this study, the ignition process and flame propagation phenomena under different EGR dilution ratios for H2/N2/O2 and CH4/N2/O2 mixtures were conducted in a constant-volume combustion chamber. The results suggested that the increase in EGR dilution weakens the influence of cellular instability and causes buoyancy instability, the latter of which could be mitigated by the passive TJI method. For the passive TJI mode, the exit time of the hot jet was delayed, and the turbulent flame speed decreased with the increase of EGR dilution ratio. Four ignition phenomena, namely jet re-ignition, flame buoyancy, re-ignition failure, and misfire, were distinctly identified. However, EGR tolerance cannot be extended by passive pre-chambers. Therefore, the pre-chamber with a scavenging system that can effectively extend the lean combustion tolerance with EGR dilution compared to SI and passive TJI was proposed. The effects of air and fuel injection quantities on ignition and flame propagation were investigated. The flame propagation velocity was positively related to the air injection mass, whereas an optimum fuel mass was required to achieve fast flame propagation. The EGR limit based on dual injections in the pre-chamber was obviously extended. Moreover, under near EGR tolerance conditions, a leaner fuel injection in the pre-chamber was required to realize successful ignition in the main chamber, as strong turbulence could cause high heat transfer loss with the cool unburnt mixture and suppress the occurrence of re-ignition.

Next-Cycle Optimal Dilute Combustion Control via Online Learning of Cycle-to-Cycle Variability Using Kernel Density Estimators

Dilute combustion using exhaust gas recirculation (EGR) presents a cost-effective method for increasing the efficiency of spark-ignition (SI) engines. However, the maximum amount of EGR that can be used at a given condition is limited by a rapid increment of cycle-to-cycle variability (CCV). This study describes a methodology to design a model-based stochastic optimal controller to adjust the cycle-to-cycle fuel injection quantity in order to reduce CCV and further extend the dilute limit. Given the complexity and chaotic nature of combustion events, the controller was enhanced with online learning in order to identify the statistical properties of combustion efficiency, which are needed to generate predictions for next-cycle events. This study showed that a kernel density estimator (KDE) can be used to learn the combustion properties in real time and can be incorporated into the feedback policy in order to calculate the optimal control command. Experimental results suggested that the dilute limit can be extended from 18.5% to 21% EGR fraction at an operating condition relevant for highway cruising. Additionally, the proposed controller can achieve a large CCV reduction with less fuel enrichment compared to previous methods, overall contributing to an increase in 0.2% indicated fuel conversion efficiency.

Simulation of In-cylinder Mixture Formation in SIDI Diesel Engine

In this paper, the in-cylinder mixture formation process of a two-stroke spark-ignition direct-injection(SIDI) diesel engine is simulated and analyzed. The effects of the shape of the combustion chamber, the injection time and the initial temperature of the engine on the mixing process and the performance of the SIDI diesel engine are analyzed. The simulation results show that the offset combustor can obviously improve the fuel economy of the SIDI diesel engine. Under the premise of constant fuel injection quantity, there is an optimal fuel injection time to make the power performance and economy of the SIDI diesel engine optimal. Increasing the initial temperature is beneficial to the atomization of diesel oil and the formation of diesel mixture in cylinder. The results will guide the engineering design of SIDI diesel engine.

Experimental analysis on the operation process of opposed-piston free piston engine generator

As a novel energy conversion device, opposed-piston free piston engine generator (FPEG) has high energy conversion efficiency, high power density, low heat transfer loss and excellent NVH performance. The opposed-piston FPEG test platform is built, and the continuous and stable operation of the prototype is realized. The influence laws of key parameters such as fuel injection timing, ignition timing, fuel injection quantity, scavenging pressure and rebound cylinder initial pressure on the performance of the system are systematically analyzed, the suitable value for the opposed-piston FPEG is determined, and the stable operation mechanism and synchronization error of the system are analyzed. It is found that there is a matching relationship between injection timing and ignition timing. The injection position should be set at 37 mm-39 mm, the ignition position should be 25–27 mm, and the injection and ignition interval should be controlled at about 12 mm. The peak in-cylinder pressure increases with the increase of fuel injection quantity, and the fuller the P-V diagram is. When the scavenging pressure is 1.5 bar and the ignition position is 25 mm-27 mm, the basic indexes have extreme points. When the ignition position is 27 mm, the peak in-cylinder pressure is the largest and the engine indicated thermal efficiency is the highest. When the initial pressure of rebound cylinder is 1.7 bar, the indicated thermal efficiency is the highest. Under the trajectory tracking control strategy, the system realizes continuous and stable operation and can deal with large cylinder pressure fluctuation. The synchronization error changes periodically and is relatively large in the middle of the expansion stroke and near the outer dead center.

Study of the Influencing Factors on the Small-Quantity Fuel Injection of Piezoelectric Injector.

The piezoelectric injection-system provides a reliable approach for precise small-quantity fuel injection due to its fast, dynamic response. Considering the nonlinearity of a piezoelectric actuator, the complete electro-mechanical-hydraulic model of the piezoelectric injector was established and verified experimentally, which showed that it could accurately predict the fuel injection quantity. The small-quantity fuel injection with different driving voltages, pulse widths, and rail pressures was analyzed. The effects of key structural parameters of the injector on the delivery, control-chamber pressure fluctuation, and small-quantity injection characteristics were studied. The results show that the linearity of the curve of the injection volume with the pulse width was relatively poor, and there was a significant inflection point when the piezoelectric injector worked in the small pulse width region (PW < 0.6 ms). The bypass valve significantly accelerated the establishment of the control-chamber pressure, reduced the pressure fluctuation in the chamber, shortened the closing delay and duration of the needle valve, and reduced the rate of the fuel-quantity change so that it provided a greater control margin for the pulse width over the same fuel volume change interval. Under the condition of a small-quantity fuel injection of 20 mm3, decreasing the inlet orifice diameter and increasing the outlet orifice diameter shortened the minimum control pulse width and fuel injection duration required for the injector injection, which is beneficial for multiple and small-quantity fuel injection. However, these behaviors reduce the control margin for the pulse width, especially in small pulse width regions.

Spray Behavior, Combustion, and Emission Characteristics of Jet Propellant-5 and Biodiesel Fuels with Multiple Split Injection Strategies

This study focuses on an analysis of the spray behavior, combustion, and emission characteristics of jet propellant-5 (JP-5) and biodiesel fuels with single-injection timing and multiple split injection strategies in a common rail direct injection (CRDI) single-cylinder diesel engine system. The analysis includes visualization of the spray and combustion. Multiple split injection strategies (e.g., double, triple, quadruple, and quintuple) were considered by equally distributing the fuel injection amount within the single-injection. Injection of biodiesel has a delayed start (0.2 ms) as well as shorter spray tip penetration compared with JP-5. As the fuel injection timing was approached to the top dead center (TDC), the engine performance and combustion efficiency improved. Retarding the injection timing contributed to an increase in carbon dioxide (CO2) (JP-5: max. 2.6% up, BD100: max. 1.5% up) and a decrease in carbon monoxide (CO) (JP-5: max. 93% down, BD100: max. 91% down) and nitrogen oxides (NOx) (JP-5: max. 83% down, BD100: max. 82% down). In comparison with JP-5, biodiesel showed disadvantages from the point of its combustion and emission characteristics for all injection timings. The quadruple-injection strategy, in which fuel injection was performed four times, showed excellent combustion, engine performance, and combustion efficiency. The CO2 emissions were highest with the quadruple-injection strategy (JP-5: 6.6%, BD100: 5.8%). The CO emissions of biodiesel decreased as the pulses of split injection extended, and a significant reduction of 83.8% was observed. NOx increased as the number of split injections increased (JP-5: max. 37% up, BD100: max. 52% up). JP-5 was a longer ignition delay than that of biodiesel from combustion flame visualization results. The final combustion in the multiple-injection strategy showed a typical diffusion combustion pattern.

Dynamic modeling of a free-piston engine based on combustion parameters prediction

A dynamic combustion model (DCM) is proposed for model-based control synthesis design in an opposed-piston free-piston engine (FPE). The DCM combines a modified triple Wiebe function with an artificial neural network (ANN), and considers the effects of engine variables such as cylinder wall temperature, fuel injection quantity and ignition timing. Firstly, it was proved by algebraic analysis that the triple Wiebe function can well describe the three combustion stages of the FPE. The ANN was then trained using the data obtained through CFD simulations at different operating points, with the aim of predicting combustion parameters based on engine variables. After the model was calibrated, it was verified by the test results from a prototype. Furthermore, this model was used to investigate combustion control strategies for cold start and stable operation. The results showed that the DCM has high precision and can simulate the complex combustion process under a wide range of FPE conditions, and is a favorable tool to make control strategies without experiments, especially in the cold start phase. Unlike general combustion modeling methods, this study provides a cost-effective way to build such a model for controller design.

Numerical research on influence of structural parameters of common-rail injector on injection rate of each nozzle hole

Performance of diesel engines are influenced by fuel spray distribution, fuel-air mixture formation and combustion, which are also influenced by hole-to-hole fuel injection rate from multi-hole injectors. In this study, a customized spray momentum flux experimental test rig was used to measure the transient injection rates from a two-layered 8-hole diesel injector. The results indicated that the fuel injection rate and the cycle fuel injection quantities of the lower-layered nozzle holes were 3–15% higher than the fuel injection rates and the cycle fuel injection quantities of the upper-layered nozzle holes. A three-dimensional (3D) computational fluid dynamics (CFD) model of the two-layered 8-hole diesel injection nozzle was developed and validated by analyzing the relative error between the numerical results obtained from the model and the experimental results measured with the test injector. The simulation results showed that the relative average deviation of hole-to-hole cycle injection quantities were less than ±1%, which is the result of 5% increment in the cross-sectional area of the upper-layered holes.

Experimental study into the effects of stability between multiple injections on the internal flow and near field spray dynamics of a diesel nozzle

To improve the control accuracy and injection stability in multiple injection processes, the coupling effects of needle valve wobbling and residual bubbles on the nozzle internal flow and near field in diesel engines were researched. And the high-speed microscopic imaging technology was employed to study the dynamics behaviors of a real-size tapered hole nozzle under different multiple injection strategies. Research results indicated that during the pre-injection and post-injection process, the difference in throttling effect caused by the wobbling of the needle valve is the main reason for the instability of the fuel injection quantities. As the pulse widths increases, the actual injection duration and the maximum needle valve lift increased, so that the throttling position changes from the passage between the needle valve and the needle seat to the nozzle holes, and two kinds of string cavitation are gradually formed. String cavitation starts at the needle valve apex and propagates outward along the nozzle wall in a sinusoidal wave trend. During the main injection stage, the spray cone angle showed a boot-shaped trend, forming a development stage, a transformation stage and a stable stage. When the needle valve rises and falls, there is air suction in the nozzle, and there is a secondary disturbance phenomenon. During the injection, the spray pattern is affected by the combined influences of the axial momentum and radial momentum of the injected fuel, resulting in a difference between the secondary disturbance and the primary breakup. When the secondary disturbance occurs, the subsequent high-speed fuel will hit the spray mass with a slow speed, which forms a vortex at both ends to develop radially, and expands the range of the spray tip.