Direct Injection Injector Research Articles

Optimization of methanol/diesel dual-fuel engines at low load condition for heavy-duty vehicles to operated at high substitution ratio by using single-hole injector for direct injection of methanol

Methanol, as a low-carbon and easily synthesizable fuel, is one of the promising directions for future internal combustion engine (ICE) fuels. However, methanol/diesel engines with high energy substitution ratios exhibit a significant drawback at low loads, namely poor fuel economy, which seriously hinders the development of dual fuel engines. Therefore, this paper conducts an optimization study on the combustion strategy of methanol/diesel in heavy-duty vehicle engines under high energy substitution ratios (70 %) and low loads. Innovatively combines single-hole injection with the direct dual fuel stratification (DDFS) technology. By coupling the longer injection duration of a single hole with higher injection pressure, and tailored combustion strategy adjustments, successfully achieving the goal of optimizing low-load methanol dual fuel engines. The research results indicate that when employing a methanol single-stage injection strategy, setting the start of diesel injection (SODI) of −25°CA after top dead center (ATDC) effectively enhances the combustion efficiency of methanol/diesel, especially when combined with a strategy that the start methanol injection (SOMI) is of −23°CA ATDC. This combination can boost the gross indicated thermal efficiency (ITEg) to 51.95 %. The research on utilizing a methanol two-stage injection strategy found that increasing the methanol premixing appropriately, within the engine's safe range, can effectively enhance ITEg. Specifically, with the methanol pre-injection ratio (MPR) of 10 % and the methanol two-stage injection interval (MII) of 20°CA, ITEg can be improved to 52.07 %. However, excessively of premixing can lead to premature combustion, causing an increase in negative work during the compression stroke and consequently reducing ITEg. This study has unveiled effective solutions for the application of methanol/diesel DDFS technology in the automotive engine field. It offers insights into the selection and optimization of methanol injectors and provides theoretical support and practical references for achieving clean and efficient combustion in engines.

The Effect of Water Injection on a Naturally Aspirated Spark-Ignited Engine

Water injection (WI) is a well-known technique to mitigate knocking phenomena, reducing the in-cylinder gas temperature with a high heat of vaporization and specific heat of water. In this study, the effect of WI directly into the cylinder on fuel efficiency was investigated using a 2.0 L naturally aspirated (NA), four-cylinder, port fuel injection (PFI)-spark-ignited (SI) engine. Spray visualization of water injection by a commercial gasoline direct-injection (GDI) injector was performed to elucidate the water evaporation characteristics. In engine experiments, combustion characteristics were analyzed by adjusting the WI timing and amount. Synergistic effects with other gas dilution techniques, such as EGR and Lean burn, were also investigated. The spray image of WI showed poor evaporation of water compared to gasoline, even at high fuel temperatures. The optimal timing of WI was advanced up to the early intake stroke due to the harsh conditions of NA engines for water evaporation compared to turbocharged engines. With the combination of EGR, the optimal WI timing was advanced by the compression stroke, and further fuel efficiency improvement was achieved. In lean combustion, WI can improve both combustion stability and fuel efficiency.

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.

Near-field plume-to-plume interaction of multi-hole GDI injector under elevated ambient density conditions

Spray collapse can occur in the multi-hole injector under elevated ambient density conditions due to the plume-to-plume interaction. Numerous studies have investigated spray collapse in high ambient density conditions, but limited literature is available regarding the near-field plume-to-plume interaction triggering the spray collapse due to the optical density of the spray in the near field. In this study, an X-ray phase-contrast imaging (XPCI) technique that can visualize the spray structure and dynamics in the near field is applied to resolve the optical difficulties. With this method, the plume-to-plume interaction of a multi-hole gasoline direct injection injector is analyzed by measuring the transverse spray droplet size and axial velocity distributions under various ambient densities and injection pressures. The results showed that in the high ambient density condition with the low injection pressure, the spray droplet size started to increase, and the axial velocity remained stagnant from around 3 mm axial location as a result of plume-to-plume interaction and following spray collapse. The region of large droplets appeared asymmetric based on the hole arrangement. As the injection pressure increased in the high ambient density condition, the plume-to-plume interaction was suppressed in the near field and the spray collapse appeared farther downstream. Through the results, the spray collapse phenomenon and associated mechanism in the near field were discussed considering the droplet collision/coalescence and pressure structure in the spray.

Effects of step hole geometry and spray-wall interactions on spray atomization in LPDI injector

The study aims to analyze the spray atomization of liquefied petroleum gas direct injection (LPDI) injector based on the macroscopic and microscopic experiments. Two experimental injectors were used in the presence and absence of step hole, and the experimental fuels used n-heptane and n-butane.The macroscopic and microscopic spray characteristics as function of the application of step hole were analyzed using two experimental injectors and n-heptane fuel. The macroscopic spray experiments analyzed the initial spray, after the end of injection and nozzle tip wetting using near-field visualization, and microscopic spray experiment analyzed fuel–air atomization phenomenon as function of the application of step hole using PDPA equipment.In addition, macroscopic and microscopic spray characteristics were analyzed for two experimental fuels and spray-wall impingement using the presence of step hole injector. The macroscopic spray experiment analyzed the spray evaporation characteristics for the two experimental fuels and spray-wall impingement using the schlieren visualization, and microscopic spray experiment analyzed the fuel–air atomization phenomenon as function of the two experimental fuels and spray-wall impingement using PDPA equipment.It was found that the presence of step hole injector showed better atomization results than those of the absence of step hole injector. But, the tip wetting of the presence of step hole injector was poor than that of the absence of step hole injector. Furthermore, based on the schlieren experiment, a comparison of free and flat sprays with the two fuels found that the spray width and area of n-heptane in free spray exceeded those of n-butane owing to the vapor pressure of n-butane. However, in the flat spray, the spray width and area of n-butane were exceeded those of n-heptane. It was found that the atomization was promoted after the spray-wall impingement.

Simulations of ammonia spray evaporation, cooling, mixture formation and combustion in a direct injection compression ignition engine

This study investigates the novel approach of direct liquid ammonia injection into the combustion chamber of a compression ignition engine. Unlike traditional gaseous ammonia port injection, this method shows promise in reducing ammonia slip and emissions. To simulate and analyze the behavior of the liquid ammonia spray, we employed numerical models based on existing literature on flashing and non-flashing spray simulations, as well as recent experimental studies on ammonia spray characteristics using a gasoline direct injection (GDI) injector. Our approach utilized a Lagrangian discrete phase modelling technique to perform a series of three-dimensional computational fluid dynamics (CFD) simulations. The primary objectives of this research were to evaluate the evaporation process of ammonia and its cooling effect, as well as to gain insights into mixture formation within the engine cylinder under different operating conditions. The simulations encompassed the entire engine cycle, considering a multi-hole GDI ammonia spray in conjunction with pilot n-heptane, a diesel surrogate, in equal proportions on an energy basis. Three distinct injection timings for ammonia were examined, leading to varying thermodynamic conditions within the combustion chamber during each spray formation. Consequently, different modelling parameters and initial conditions were necessary to accurately replicate the spray behavior. To address this, we proposed a systematic procedure for assigning pre-defined spray angles. The non-reacting, evaporating spray simulations yielded valuable insights into the mixture formation process, which guided our analysis. Finally, reacting conditions were considered to evaluate engine performance and resulting exhaust gas emissions. This study provides a comprehensive overview of critical aspects related to direct ammonia injection in internal combustion engine (ICE) systems. Moreover, it uncovers performance trends that can serve as a foundation for future investigations in this field.

Investigations on reactivity controlled compression ignition combustion with different injection strategies using alternative fuels produced from waste resources

Reactivity-controlled compression ignition (RCCI) is a promising low-temperature combustion (LTC) strategy that results in low oxides of nitrogen (NOx) and soot emissions while maintaining high thermal efficiency. At the same time, RCCI leads to increased unburned hydrocarbon (HC) and carbon monoxide (CO) emissions in the exhaust, particularly under low loads. The current work experimented novel port-injected RCCI (PI-RCCI) strategy to overcome the high unburned emission limitations at low load conditions in RCCI. PI-RCCI is a port injection strategy in which low-reactivity fuel (LRF) is injected using a low-pressure injector, and the high-reactivity fuel (HRF) is injected through a high-pressure common rail direct injection (CRDI) injector. The low volatile HRF is injected into a heated fuel vaporizer maintained at 180°C in the intake manifold during the suction stroke. Modifying a single-cylinder, light-duty diesel engine with the necessary intake and fuel injection systems allows engine operation in both RCCI and PI-RCCI modes. Alternative fuels from waste resources such as waste cooking oil biodiesel (WCO) and plastic waste oil (WPO) are used as the HRF and LRF fuel in RCCI and PI-RCCI. To achieve maximum thermal efficiency in RCCI, the premixed energy ratio and the start of injection of the direct-injected fuel are optimized at all load conditions. The engine performance and exhaust emissions characteristics in PI-RCCI are compared with RCCI as a baseline reference. The results show a 70% and 48% reduction in CO and HC emissions, respectively, in PI-RCCI than in RCCI. Further, the brake thermal efficiency (BTE) was enhanced by around 20%, and the brake-specific fuel consumption (BSFC) was reduced by 13% in PI-RCCI. The NOx emissions decreased without any considerable changes in soot emission in PI-RCCI. The current study shows that fuels derived from waste resources can be used in RCCI and PI-RCCI modes with better engine performance and lower emissions.

Correlating armature and needle dynamics with voltage waveforms of solenoid-actuated GDI injector

The injector voltage hump that appears near the needle closing has been used for the real-time monitoring and feedback control of fuel injection duration in modern engines. This voltage hump has been thought to result from the abrupt change in electromagnetic induction by the stoppage of needle motion but detailed electromagnetic processes and associated armature and needle dynamics during the needle closing have not been thoroughly investigated in a wide range of injection conditions, which knowledge is crucial for the delicate control of fuel injection based on the voltage hump. The current study analyzes the transient armature and needle dynamics of a solenoid-actuated gasoline direct injection injector using an X-ray phase-contrast imaging technique. Then, the results are correlated with voltage waveforms during the needle closing transient under various injection pressures, injection pulse durations, and dwell times of split injections. The time derivatives of voltage waveforms showed lower and upper peaks in order in the regime of the voltage hump. Inconsistent with conventional understandings, the lower peak timing of the voltage derivative did not match with the timing of needle closing (end of injection) but rather matched with the abrupt descent timing of the armature and needle. The inflection timing and upper peak timing of the voltage derivative matched with the timings of actual needle closing and armature closing respectively. The amplitude of the voltage hump was near linearly dependent on the needle closing speed. The needle closing speed decreased upon the decrease of injection pulse duration and injection pressure which made it difficult to detect the voltage humps in ballistic injection regimes and low injection pressures. In split injection conditions, the voltage hump of the first injection was not detectable if the dwell time was shorter than the needle closing delay, the time from the current cut-off to the actual needle closing.

Study on predictions of spray target position of gasoline direct injection injectors with multi-hole using physical model and machine learning

A lot of effort is being invested in improving the performance of injectors, the core components of gasoline direct injection (GDI) engines, such as injection stability and accuracy. The purpose of this study is to establish models that can predict spray targeting according to the design parameters of GDI injector, to improve the injection accuracy and enhance the engine performance. First, this study used laser sheet beam visualization technology to measure the spray targeting images of injectors with different design parameters in different cross-sections and obtained the spray targeting coordinates through image post-processing. Then, using the experimental data, two different approaches (empirical formula and machine learning), were used to create models for predicting spray targeting, and their applicability was compared. The research results showed that both the physical model and the machine learning model had a prediction accuracy of >0.98 in terms of R2, but the physical model had a lower prediction error in terms of the root mean square error (RMSE). Further, the tendency of the target coordinate to change is proportional to 0.2 power of the injection pressure (Pinj0.2), −0.1 power of ratio of hole length to hole diameter ((L/D)−0.1), and − 1.5 power of the angle between axes of two holes (θij−1.5).

Effects of in-nozzle flow and low-pressure zone on spray targeting of multi-hole gasoline direct injection injector

The purpose of this study is to reveal the effect of In-nozzle flow and low-pressure zone near the nozzle exit on the spray targeting of a multi-hole gasoline direct injection injector using a numerical simulation. The change in spray targeting owing to in-nozzle flow and the distribution of the liquid phase at the hole exit were analyzed through a multi-phase flow simulation. A volume of fluid (VOF) model was used to effectively distinguish between the liquid flow and cavitation region. Results of the numerical simulation at the internal and near-field show that cavitation occurred at a sharp corner with a high flow velocity. Moreover, the low liquid rebounded at the hole wall, and the flow was bent in the direction of cavitation. The results of the spray simulation indicated that an increase in the injection pressure reduced the minimum pressure in the low-pressure zone. By contrast, the increase in ambient pressure not only decreased the pressure in the low-pressure zone, but also caused the low-pressure zone to form closer to the hole exit. In most cases, the low-pressure zone had a greater effect on plume bending than on in-nozzle flow, which was further enhanced as the ambient pressure increased.

Comprehensive investigation on ballistic injection characteristics of GDI injector: A particular focus on injection pressure and fuel effects

The ballistic injection occurs in the short injection pulse conditions of solenoid-actuated fuel injectors, in which the injection mass does not have a linear relationship with the coil energizing time (injection pulse duration). Sometimes, a reversal stage appears in the ballistic regime in which the injection mass temporarily decreases against the increase of injection pulse duration. Previous studies have observed these nonlinear injection characteristics but insufficient attention has been paid to what are the related mechanisms and how they appear differently based on injection parameters. Understanding these is of great importance for the advanced design and control of fuel injectors in conventional and alternative fuel engines, particularly applying the short-pulse multiple injection strategies. The current study investigates the injection pressure and fuel effects on ballistic and linear injection characteristics of a gasoline direct injection injector using a Bosch long-tube injection rate meter. In the long-pulse linear injection regime, the injection pressure effect showed a typical trend but the fuel effects appeared insignificant. However, these injection pressure and fuel effects appeared more complicated and dramatic in the ballistic regime. The increase in the injection pressure showed a slower needle rise which caused a shorter injection duration and the appearance of the reversal stage at a longer injection pulse duration. The higher fuel viscosity caused a longer injection delay, which resulted in a shorter injection duration, lower injection mass, and the appearance of the reversal stage at a longer injection pulse duration. The needle dynamics associated with the ballistic injection characteristics and their dependence on injection parameters were thoroughly discussed based on the results.

Influence of Elevated Fuel Temperatures On the Spray Characteristics of Gasoline - Ethanol Blends

Abstract In this study, the effect of elevated fuel temperatures on the spray characteristics of gasoline-ethanol blends were studied in an optically accessible constant volume spray and combustion vessel. MAHLE SmartHeat® is a fuel heater located directly upstream of the fuel injector. High speed images of the spray injected from a six-hole gasoline direct injection injector typical of a side-injection engine were captured with shadowgraph imaging technique. Two fuel blends, gasoline with 10% ethanol (E10) and 85% ethanol (E85) were investigated at ambient conditions of 1 bar, 45°C and 4 bar, 180°C at an injection pressure of 100 bar. Fuel temperatures were varied from 75 to 250°C. A comparison of the near nozzle and the global spray characteristics was made for the two fuels in the range of fuel temperatures selected. Results showed that flash boiling leads to two primary effects for the two fuel blends: (i) an appreciable increase in spray angle near the exit of the nozzle followed by (ii) a decrease in spray angle downstream of the nozzle due to the interaction of the plumes and the collapsing of the spray. Furthermore, for both fuel blends, upon flash boiling, entrainment and mixing were reduced downstream of the nozzle because of the collapse of the spray. To reduce this effect, nozzle orientations and geometries should be modified.

Predictions and analysis of flash boiling spray characteristics of gasoline direct injection injectors based on optimized machine learning algorithm

The main purpose of this study is to make a machine model that can predict the characteristics of flash boiling spray according to the injector design parameters and the injection conditions, and then use the machine learning model to further analyze the spray characteristics. In order to achieve described purpose, this study uses three decision tree algorithms (random forest (RF), gradient boosted regression tree (GBRT) and extreme gradient boosting (XGB)) to build machine learning models, and utilizes the tree-structured parzen estimator (TPE) for farther improvement of models' performance. The influence of injector design parameters and injection conditions on spray characteristics was analyzed, basing on the constructed machine learning model. Finally, the spray characteristic map was made by predicting the spray characteristics under 1 million conditions, and the method of using the spray characteristic map to design the spray characteristics was proposed. The results have shown that TPE-GBRT has the most accurate prediction result for spray tip penetration (STP), and TPE-XGB has the most accurate result for spray downstream angle (SA_down). The feature importance analysis indicated the greater importance of the injection conditions over the injector design parameters for the spray characteristics. Further, by analyzing the spray characteristics map, the injection conditions have less design freedom, while injector parameters can assume different values to achieve the same spray characteristics.

Characterizing under-expansion behaviors induced by rapid phase change of flash-boiling jets

Flash-boiling sprays issued from multi-hole gasoline direct injection (GDI) injectors could collapse, which is recently proved to be caused by under-expansion, but very few experimental data are available on this sort of under-expansion. In this study, high-speed microscopic Schlieren photography was used to capture the near-field shock structures in flash-boiling n-hexane jets. The tests were carried out in a constant volume vessel with ambient pressures (Pamb) from 10 to 101 kPa, fuel temperatures (Tfuel) from 30 to 170 ℃, and injection pressures (Pinj) from 2 to 20 MPa. The shock structure was carefully analyzed in terms of shock width and length. Generally, both the shock width and length decreased with the increase in Pamb. With the increase in Tfuel, the shock length was relatively stable and the shock width overall increased, but a decreasing trend in shock width could be observed at 170 ℃, possibly caused by the near-critical behaviors. Further analysis showed that the shock width shows a strong linear correlation with Δμ·Pamb−0.5 (Δμ denoting chemical potential of phase change) for a given Pinj, and the shock length shows a strong quadratic polynomial relationship with ηinj (injection pressure ratio, defined as the ratio of Pinj to Pamb). Additionally, some new shock structures without Mach disk were observed, indicating that the phase change induced under expansion is different from the typical gaseous under-expansion.

Correlation between needle behavior and fuel flow rate for gasoline direct injection injector using X-ray phase contrast imaging technique

To meet strong emission regulations such as Euro-7, which is expected to be implemented in 2025. The multiple-injection strategy is one of well-known solutions to reduce exhaust gas and improve combustion performance on GDI engine. In order to realize multiple-injection strategy, it is necessary to secure excellent flow rate repeatability within short period. Therefore, the purpose of this study was to analyze the flow rate repeatability of GDI injector under various multiple injection conditions and to correlate with needle behavior of GDI injector and flow rate repeatability. To analyze flow rate repeatability, the injection rate data was obtained by the Bosch method and the individual flow rates of 110 shots were analyzed under several experimental conditions. The movements of the ball and armature inside the injector were visualized using the X-ray phase contrast imaging (XPCI) technique, and the individual behaviors of the ball and the armature were quantitatively analyzed by image post-processing analysis. In this study were used two test GDI injectors with same structure. Whereas Flow rate results were different on shorter dwell time conditions. This study revealed that a specific injector had unstable injection rate and worse Shot to Shot (STS) deviation under dwell time 0.7 ms. In addition, armature bouncing appeared in a specific GDI injector. This armature bouncing affects unstable flow rate characteristics because when armature lift up again, the position of armature was different at every time.

Spray Collapse in a Side-mount Gasoline Direct Injection Injector with Various Injection Conditions and Injector Nozzle Configurations

Spray Collapse in a Side-mount Gasoline Direct Injection Injector with Various Injection Conditions and Injector Nozzle Configurations

Experiment methods and apparatus for finely controlled partial needle lift measurements with a gasoline direct injector

In this study, an experiment method and apparatus are developed which allow exploration of partial-lift spray in a production gasoline direct injection (GDI) injector. For this injector, discretizing the needle’s stroke into a series of steady partial-lift tests seems a viable approach for quantifying transient behavior, where spray performance is often inferior from the perspective of emissions. However, performing such tests is not trivial due to manufacturing challenges and material limitations making it difficult to isolate any particular lift at pressure. To explore the applicability of fixed partial-lift tests, the following are performed: (1) An inward-opening multi-hole GDI injector is minimally modified with an apparatus to finely control needle lift by limiting the needle’s stroke with a fine micrometer head. (2) An experiment process is developed to associate the micrometer set-point with the imposed needle lift, compensating for pressure induced component flex. This flex is significant and of a similar magnitude to the needle’s stroke. (3) In-nozzle flow is simulated using computational fluid dynamics (CFD) within the AVL FIRE software to compare a stationary and moving needle. The comparison reveals a relative insignificance of needle velocity for the majority of the needle’s stroke (>5 μm). The nozzle hole flow rates and effective exit velocities are similar, suggesting fixed partial-lift spray well approximates the normally moving needle spray. This new experiment method can be used on current injectors to quantify spray performance during needle transients by discretizing the stroke into steps as small as 2 μm, exceeding the control in any current published literature.

Spray collapse characteristics of practical GDI spray for lateral-mounted GDI engines

Spray collapsing and plume merging processes were investigated using a lateral-mounted gasoline direct injection (GDI) injector with a practical 'triangular' spray pattern. High-speed diffusive back illumination extinction imaging followed by computed tomography reconstruction was applied to understand the spatiotemporal plume dynamics under engine-like conditions. The spray chamber and injector conditions include (1) cold, subcooled standard temperature and pressure (STP) used by the injector manufacturer, (2) practical gasoline fuels with full-range distillation, (3) flash-boiling with fuel temperature and vacuum gas pressure, and (4) high gas pressure and temperature typical of injection during compression. The novel experiments permit tracking of plume merging at different times and axial distances downstream of the nozzle. A triangular 6-hole pattern, which is widely used in lateral-mounted GDI engines, was found to be prone to having the centrally located plumes move close to each other thus leading to spray collapse with these plumes at all practical test conditions (2)–(4). Variations of air entrainment and local pressure with different conditions were identified as dominant factors for the timing and position of spray collapse.

Development of Primary Breakup Model with Internal and Near-Field Simulation to Predict Spray Collapse of Gasoline Direct Injection (Gdi) Injector

Development of Primary Breakup Model with Internal and Near-Field Simulation to Predict Spray Collapse of Gasoline Direct Injection (Gdi) Injector

Correlation between Needle Behavior and Fuel Flow Rate for Gasoline Direct Injection Injector Using X-Ray Phase Contrast Imaging Technique

Correlation between Needle Behavior and Fuel Flow Rate for Gasoline Direct Injection Injector Using X-Ray Phase Contrast Imaging Technique