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The present research analyses the injection rate of a direct rail injection diesel engine, focusing specifically on the influence of the nozzles and various operating conditions from real road tests on the rate of injection. A diesel injector test bench was used for feedback with real data from the test vehicle under real road conditions. An analysis of the behaviour of the injection rate was carried out using the zero-dimensional model. This model generated a predictive model that incorporated the five variables identified through a developed multivariate analysis of variance, showing a high correlation of dependence between variations in injection pressure, the diameter of the holes, and the number of holes with greater representativeness. The results obtained showed that the nozzle geometry and the physical properties of the fuel had a direct effect on the injection rate. This analysis enriches the understanding of fuel injection and its effects on diesel engine performance by providing an analysis of the system components that influence the injection rate and generating a simple tool to feed thermodynamic diagnostic models. The proposal model may be used as an input in thermodynamics predictive models and reduce the simulation load in computational fluid dynamics predictive models. [ABSTRACT FROM AUTHOR]

This paper presents a fuel injection rate predictive model based on zero-dimensional correlations from experimental results. This model estimates the fuel injection rate behavior with varying parameters such as fuel injection pressure-injector energizing, the injection nozzle geometrical characteristics, and fuel viscosity. The model approach was carried out with diesel fuel. Then, the model was applied to the use of two alternative low-carbon fuels without diesel. An experimental methodology was used under controlled conditions, employing an injection rate indicator to measure the injection parameters in real time. The setup was carried out on a pump test bench using a common rail injection system. The results show that the model can be adapted to different injection conditions and fuels. [ABSTRACT FROM AUTHOR]

The present research analyses the injection rate of a direct rail injection diesel engine, focusing specifically on the influence of the nozzles and various operating conditions from real road tests on the rate of injection. A diesel injector test bench was used for feedback with real data from the test vehicle under real road conditions. An analysis of the behaviour of the injection rate was carried out using the zero-dimensional model. This model generated a predictive model that incorporated the five variables identified through a developed multivariate analysis of variance, showing a high correlation of dependence between variations in injection pressure, the diameter of the holes, and the number of holes with greater representativeness. The results obtained showed that the nozzle geometry and the physical properties of the fuel had a direct effect on the injection rate. This analysis enriches the understanding of fuel injection and its effects on diesel engine performance by providing an analysis of the system components that influence the injection rate and generating a simple tool to feed thermodynamic diagnostic models. The proposal model may be used as an input in thermodynamics predictive models and reduce the simulation load in computational fluid dynamics predictive models.

This paper presents a fuel injection rate predictive model based on zero-dimensional correlations from experimental results. This model estimates the fuel injection rate behavior with varying parameters such as fuel injection pressure-injector energizing, the injection nozzle geometrical characteristics, and fuel viscosity. The model approach was carried out with diesel fuel. Then, the model was applied to the use of two alternative low-carbon fuels without diesel. An experimental methodology was used under controlled conditions, employing an injection rate indicator to measure the injection parameters in real time. The setup was carried out on a pump test bench using a common rail injection system. The results show that the model can be adapted to different injection conditions and fuels.

In this study, the injection processes and spray behavior of diesel fuel (DF), rapeseed oil (RO) and their fuel blends (RO25, RO50, RO75) have been qualitatively and quantitatively analyzed to identify the differences in the injection rate and the spray parameters. The volumetric and mass injection rates, the spray penetration, the spray cone angle and the spray area under non-evaporation conditions in a nitrogen-filled camber were analyzed. The results showed that rapeseed oil leads to a decrease in the peak injection rate due to its higher density and viscosity. Moreover, rapeseed oil and its blends with mineral diesel oil exhibited smoother rising slopes at the start of injection. The spray tip penetration was the longest for the rapeseed oil and the spray tip penetrations of the fuel blends RO25, RO50 and RO75 were arranged between the values of DF and RO. As the injection pressure increased, the differences in the spray tip penetrations diminished. Increasing the amount of rapeseed oil in fuel blends resulted in a smaller spray cone angle compared to diesel fuel. The spray area of all tested fuels increased significantly with increasing spray tip penetration, the spray area of RO was consistently lower than that of diesel fuel. [ABSTRACT FROM AUTHOR]

In this study, the injection processes and spray behavior of diesel fuel (DF), rapeseed oil (RO) and their fuel blends (RO25, RO50, RO75) have been qualitatively and quantitatively analyzed to identify the differences in the injection rate and the spray parameters. The volumetric and mass injection rates, the spray penetration, the spray cone angle and the spray area under non-evaporation conditions in a nitrogen-filled camber were analyzed. The results showed that rapeseed oil leads to a decrease in the peak injection rate due to its higher density and viscosity. Moreover, rapeseed oil and its blends with mineral diesel oil exhibited smoother rising slopes at the start of injection. The spray tip penetration was the longest for the rapeseed oil and the spray tip penetrations of the fuel blends RO25, RO50 and RO75 were arranged between the values of DF and RO. As the injection pressure increased, the differences in the spray tip penetrations diminished. Increasing the amount of rapeseed oil in fuel blends resulted in a smaller spray cone angle compared to diesel fuel. The spray area of all tested fuels increased significantly with increasing spray tip penetration, the spray area of RO was consistently lower than that of diesel fuel.

In reactivity-controlled compression ignition (RCCI) engines, the ignition and combustion of premixed low reactive fuel (LRF) such as natural gas (NG) is controlled by the injection of high reactive fuel (HRF) such as diesel fuel during the compression stroke. In this study, the effects of six different input parameters on the performance and emissions of the natural gas/diesel fueled RCCI engine are studied using fractional factorial design (FFD) method, which is one of the design of experiment (DOE) methods. In this method, the effects of the interactions of input parameters, referred to as "factors," on the outputs, referred to as "responses," are investigated. The factors include premixed ratio (PR), start of first injection (SOI1), spray angle (SA), exhaust gas recirculation (EGR), start of second injection (SOI2), and mass fraction of first injection. Sixteen runs were conducted to evaluate the effects of the interaction between input factors on performance and emissions of a RCCI engine using a validated computational fluid dynamics (CFD) model. DOE results indicate that in order to increase gross indicated efficiency (GIE), higher premixed ratio, 85%, with wider spray angle, 150°, is an effective way. Meanwhile, carbon monoxide (CO) and unburned hydrocarbons (UHC) emissions as well as ringing intensity (RI) are decreased at this condition. To reduce NOx emissions, it is beneficial to raise premixed ratio from 55% to 85% or to use 40% EGR, independently. [ABSTRACT FROM AUTHOR]

As legislations set very stringent environmental and fuel economy standards, researchers have pushed into a continuous development in all areas of the diesel engine. The recent evolution of the injection technologies has permitted to modify the fuel-delivery strategies. From what was a single pulse per injection event, modern systems allow to inject up to eight different times precisely per combustion cycle. In such sense, experimental results of the rate of injection and momentum flux could be useful for validation and improvement of computational models. Moreover, accurately quantifying the injected mass per pulse in a fuel–gas interface can provide data with more realistic engine-like conditions. To this end, this research presents measurements of the rate of injection and momentum flux for two simple multiple injection strategies: a pilot-main and a main-post. Boundary conditions included two rail and discharge pressures, two different pilot/post quantities and four dwell times. A new approach was employed to estimate the mass allocation with the momentum flux data, and results were compared to the rate of injection traces to verify the distribution calculated. On the results, signals for each pulse were successfully decoupled using its rising and falling edge. The shot-to-shot variability of the pilot/post injection was highly dependent on its transitory characteristics, and on the dwell time for post injections due to internal pressure waves. The injected mass per pulse was successfully measured as well in the momentum flux test rig, and the energizing time changed slightly to account for the different operation interfaces. Signals from both measurement campaigns showed a remarkable agreement when compared, ascertain the possibility of measuring the injected mass, and its allocation for multiple injection strategies, in the momentum flux test rig. [ABSTRACT FROM AUTHOR]

• An implicit and compressible pressure-based multi-fluid solver has been developed for the simulation of cavitating flows. • This allows to resolve pressure waves generated from the collapse of vapor bubble clouds and impacting the nearby walls. • Eroded injector simulation shows reduced mass flow rate and vapor formation compared to the nominal geometry. • The recorded pressure peaks on the nominal geometry fit well with the eroded regions of the experiments. • Lagrangian spray simulations show clear differences in spray angle and shape between eroded and nominal geometries. The consequences of geometry alterations in a diesel injector caused by cavitation erosion are investigated with numerical simulations. The differences in the results between the nominal design geometry and the eroded one are analyzed for the internal injector flow and spray formation. The flow in the injector is modeled with a three-phase Eulerian approach using a compressible pressure-based multiphase flow solver. Cavitation is simulated with a nonequilibrium mass transfer rate model based on the simplified form of the Rayleigh–Plesset equation. Slip velocity between the liquid-vapor mixture and air is included in the model by solving two separate momentum conservation equations. The eroded injector is found to result in a loss in the rate of injection but also lower cavitation volume fraction inside the nozzle. The injected sprays are then simulated with a Lagrangian method considering as initial conditions the predicted flow characteristics at the exit of the nozzle. The results obtained show wider spray dispersion for the eroded injector and shorter spray tip penetration. [ABSTRACT FROM AUTHOR]

An experimental study was performed to explore the influence of dwell time on the hydraulic interactions between injection events using pilot injection strategy, split injection strategy, post injection strategy and a solenoid diesel injector. To do so, a sweep of dwell time from 0.55 up to 2 ms using all multiple injection strategies and levels of rail pressure, of 80, 100 and 120 MPa, and single level of back pressure, of 5 MPa, was performed. The hydraulic interactions between injection events were characterized through the second injection hydraulic delay and second injection mass in an injection discharge curve indicator equipped with all the components required for its operation and control. In order to define the operating conditions of the multiple injection strategies, to ensure the same injected fuel mass in all cases, the characteristic curves of injection rate for the solenoid diesel injector studied were obtained. The second injection hydraulic delay increases with dwell time values in the range of 0.55–0.9 ms for all multiple injection strategies and levels of rail pressure tested. Conversely, the second injection hydraulic delay decreases with dwell time values higher than 0.9 ms. Moreover, the second hydraulic delay depends mainly on the dwell time and not on the injected fuel mass during the first injection event. The second injection mass increases with dwell values less than 0.6 ms. By contrast, the second injection mass is not significantly affected by that of the first injection at a dwell time higher than 0.6 ms.

Abstract The need for improved engine efficiencies has motivated the development of high-pressure combustion systems, in which operating conditions achieve and exceed critical conditions. Associated with these conditions are strong variations in thermo-transport properties as the fluid undergoes mixing and phase transition, and two-stage ignition with low-temperature combustion. Accurately simulating these physical phenomena at real-fluid environments remains a challenge. This study examines a diffuse-interface method for simulating the injection and ignition of n -dodecane at transcritical conditions. To this end, a compressible solver with a real-fluid state equation and finite-rate chemistry is employed. Simulations of an ECN-relevant diesel-fuel injector are performed for both inert and reacting conditions. For the spray ignition, four specific operating points (corresponding to ambient temperatures between 900 K and 1200 K) are investigated to examine effects of the real-fluid environment and low-temperature chemistry. Comparisons with available experimental data demonstrate that the presented numerical method adequately captures the diesel fuel injection and auto-ignition processes under transcritical conditions. [ABSTRACT FROM AUTHOR]

Highlights • A double-pilot and two triple-pilot diesel injection strategies are compared. • The triple-pilot injection strategies significantly reduce the combustion noise. • The occurence frequency of the local heat release rate (HRR) peaks matches strong frequencies responsible for combustion noise. • A new metric, the Ratio of Reduced Heat Release (RRHR) is developed for HRR analysis. • Combustion noise is reduced by reducing the RRHR, making a more linear HRR. Abstract Three injection strategies are compared in a light-duty (LD) diesel engine at a medium load point. One strategy, representative of a Euro 6 LD injection strategy, has a double-pilot/main/single-post sequence. There is a modest temporal spacing after the first pilot and second pilot. Additional strategies add a third pilot and greatly reduce the spacing after the pilots. These pilots are referred to as being "closely-coupled" to each other and the main injection. For the double-pilot strategy, there is significant undulation of the cylinder pressure around TDC. In contrast, the closely-coupled triple-pilot strategies show notably smaller undulations in their pressure traces. Despite increases in peak pressure rise rate, combustion noise is reduced in both triple-pilot strategies. An analysis of each strategy's heat release rate (HRR) trace shows that the close spacing of the pilot injections drastically reduces the drop in HRR between each subsequent local peak in combustion from each injection. A new metric is developed in order to quantify these drops, called the Ratio of Reduced Heat Release (RRHR). It is found that in order to reduce combustion noise, the RRHR should be minimized. Further analysis into the combustion noise shows that the occurence frequency of the local HRR peaks matches strong frequencies responsible for combustion noise, and furthermore that the reduction in combustion noise is not due to the geometry of the combustion chamber. The modification of the HRR trace by implementing closely-coupled triple-pilot injection strategies allows combustion to be phased earlier, improving efficiency while also reducing combustion noise. [ABSTRACT FROM AUTHOR]

The presented paper aims to study the influence of mineral diesel fuel and synthetic Gas-To-Liquid fuel (GTL) on the injection process, fuel flow conditions, and cavitation formation in a modern common-rail injector. First, the influence on injection characteristics was studied experimentally using an injection system test bench, and numerically using the one-dimensional computational program. Afterward, the influence of fuel properties on internal fuel flow was studied numerically using a computational program. The flow inside the injector was considered as multiphase flow and was calculated through unsteady Computational Fluid Dynamics simulations using a Eulerian–Eulerian two-fluid approach. Finally, the influence of in-cylinder back pressure on the internal nozzle flow was studied at three distinctive back pressures. The obtained numerical results for injection characteristics show good agreement with the experimental ones. The results of 3D simulations indicate that differences in fuel properties influence internal fuel flow and cavitation inception. The location of cavitation formation is the same for both fuels. The cavitation formation is triggered regardless of fuel properties. The size of the cavitation area is influenced by fuel properties and also from in-cylinder back pressure. Higher values of back pressure induce smaller areas of cavitation and vice versa. Comparing the conditions at injection hole exit, diesel fuel proved slightly higher average mass flow rate and velocities, which can be attributed to differences in fluid densities and viscosities. Overall, the obtained results indicate that when considering the injection process and internal nozzle flow, GTL fuel can be used in common-rail injection systems with solenoid injectors.

The injection rate curve is an important input parameter in the thermodynamic diagnosis and in the predictive models, and it can also be used to simulate fuel sprays under different operating conditions. In this work, a zero-dimensional fuel injection rate model is proposed from experimental data obtained from a common-rail injection system with two solenoid-operated injectors. The model proposed is a useful tool when the internal component's dimensions of the injector are unknown. The presented model only requires the injection pressure, the injector energization signal, the total fuel mass consumed per stroke, the geometry and the holes number of the fuel injector and, finally, some physical properties of fuel. The model has been applied to two different solenoid-operated injectors and two fuels. The comparative results between the experimental and the modelled fuel injection rate show excellent results despite the simplicity of the experimental data requirements. The effects of the introduction of the modelled and measured fuel injection rate in a thermodynamic diagnostic tool are shown. This proposed model can be a useful, simple and alternative tool for estimating rates of injection without the need to carry out a test of the rate of injection. [ABSTRACT FROM AUTHOR]

The aim of this paper is to identify and investigate the potential and limitations of diesel-gas combustion concepts for high speed large engines operated in gas mode with very small amounts of pilot fuel (<5% diesel fraction). Experimental tests were carried out on a flexible single cylinder research engine (displacement 6.24 dm³) equipped with a common rail system. Various engine configurations and operating parameters were varied and the effects on the combustion process were analyzed. The results presented in this paper include a comparison of the performance of the investigated dual fuel concept to those of a state-of-the-art monofuel gas engine and a state-of-the-art monofuel diesel engine. Evaluation reveals that certain limiting factors exist that prevent the dual fuel engine from performing as well as the superior gas engine. At the same NOx level of 1.3 g/kWh, the efficiency of the dual fuel engine is ≈3.5% pts. lower than that of the gas engine. This is caused by the weaker ignition performance of the injected pilot fuel compared to that of the gas scavenged prechamber of the gas engine. On the other hand, the dual fuel concept has the potential to compete with the diesel engine. The dual fuel engine can be operated at the efficiency level of the diesel engine yet with significantly lower NOxemissions (3.5 g/kWh and 6.3 g/kWh, respectively). Since the injection of pilot fuel is of major importance for flame initialization, and thus for the main combustion event of the dual fuel engine, optical investigations in a spray box, measurements of injection rates, and three-dimensional (3D) computational fluid dynamics (CFD) simulation were conducted to obtain even more detailed insight into these processes. A study on the influence of the diesel fraction shows that diminishing the diesel fraction from 3% to lower values has a significant impact on engine performance because of the effects of such a reduction on injection, ignition delay, and initial flame formation. The presented results illustrate which operating strategy is beneficial for engine performance in terms of low NOx emissions and high efficiency. Moreover, potential measures can be derived which allow for further optimization of the diesel-gas combustion process. [ABSTRACT FROM AUTHOR]

As the regulations for pollutant emissions in diesel engines are increasingly restrictive, the introduction of the piezoelectric direct-acting injectors seeks to improve the overall efficiency of the injection system, and consequently reduce combustion contaminants. In such systems, the needle lift is governed by the charge, or voltage, applied to the piezo stack, allowing for a more precise control over the fuel injection process. Although it is known that the performance of the piezoelectric crystals depends on its temperature of operation, the effect this has on the rate of injection is still unclear. In this research, a particular setup was used to measure the rate of injection of a direct-acting injector for different operating temperatures. It was mounted into an injection discharge rate curve indicator with a particular holder that has a cooling sleeve connected to a circuit running ethylene glycol, which is driven by a thermoregulator unit. A parametric sweep of different piezo stack control voltages for three rail pressures and operating temperatures was carried out. On the results, when needle lift does not influence internal flow development, the rate of injection was controlled by the injection pressure, with minimal impact from the working temperature, resembling results from conventional hydraulic injectors. At partial needle lift, two operating regions were observed, delimited by a particular voltage level. Above it, the needle throttling was able to control mass fuel flow accurately. But below it, the stabilized rate of injection values decreased drastically. The rate of this decline was dependent only on the injection pressure. The threshold level, named critical voltage, increased linearly with increasing injection pressure and working temperature. Also, to maintain a constant fuel mass flow for decreasing operating temperature, the voltage level of the control signal had to be reduced. These results highlight the importance of monitoring and controlling the operating conditions of the direct-acting injectors, as their performance and efficiency are both influenced by the working temperature of the piezo stack. [ABSTRACT FROM AUTHOR]

In this paper, lift-off length has been measured via both broadband luminosity and OH chemiluminescence. In addition, ignition delay has also been measured via broadband chemiluminescence and Schlieren imaging. A 3 orifice injector from the Engine Combustion Network (ECN) set, referred to as Spray B, and a single component fuel (n-dodecane) was used. Experiments were carried out in a constant flow and pressure facility, that allowed to reproduce engine-like thermodynamic conditions, and enabled the study to be performed over a wide range of test conditions with a very high repetition rate. Data obtained was also compared with results from a single orifice injector also from the Engine Combustion Network, with analog orifice characteristics (90 μm outlet diameter and convergent shape) and technology as the injector used. Results showed that there is good correlation between the ignition delay measured through both methodologies, that oxygen concentration and injection pressure plays a minor role in the ignition delay, being ambient temperature and density the parameters with the highest influence. Lift-off length measurements showed significant differences between methodologies. Minor deviation was observed between injectors with different nozzle geometry (seat inclination angle), due to temperature variations along the chamber, highlighting the importance of temperature distribution along combustion vessels. Empirical correlations for lift-off and ignition delay were calculated, underlining the effect of the conditions on the parameters studied. Coefficients of the correlations were compared with results for the single orifice injector, this showed that variations of test conditions have the same impact on ignition delay and lift-off length regardless the nozzle orifice configuration. [ABSTRACT FROM AUTHOR]

Waste cooking oil (WCO) was experimentally examined to determine whether it can be used as an alternative fuel in a 3-cylinder, 4-stroke, direct injection, 48 kW power tractor engine. The test engine was operated under full load conditions using diesel fuel and waste vegetable oil from the 2400 to 1100 rpm and performance values were recorded. Tests were performed in two stages to evaluate the effect of the waste oils on the engine life cycle. When the test engine was operated with diesel fuel and waste cooking oil; engine torque decreased between at ratio of 0.09 % and 3% according to the engine speed. While no significant difference occurs in the diesel fuel tests at the end of 100 hours of operation, an important reduction was observed in the engine torque of the WCO engine between 4.21% and 14.48% according to the engine speed, and an increase in average smoke opacity ratio was also observed. In accordance with the results obtained from the studies, it was determined that the engine performance values of waste cooking oil show similar properties with diesel fuel, but in long-term usage, performance losses increased. In the SEM analysis performed on the fuel system, there were dark deposits at the nozzle tip and stem. According to an EDX analysis at the nozzle tips, the detected elements point to engine oil ash in the combustion chamber and show coking products (C and O). The other elements (Na, S, Ca, P, Cl, and K) point to used WCO. [ABSTRACT FROM AUTHOR]

Understanding and controlling mixing and combustion processes is fundamental for the ever more demanding pollutant regulations and fuel consumption standards of direct injection diesel engines. The fundamentals of these processes have been long studied from both experimental and numerical perspectives. As numerical models become more advanced, the need for adequate experimental data increases. Hence, experimental methodologies and scientific databases need to be enhanced with more quantitative, accurate, consistent, and reliable information in order to evaluate the models in a robust fashion. The present study seeks to enhance the current state-of-the-art by further evaluating the combustion performance of a two-component diesel surrogate for multi-dimensional compression ignition engine simulations, composed of n-dodecane and m-xylene. This surrogate is expected to better represent diesel fuel combustion than the standard Engine Combustion Network (ECN) fuel (n-dodecane), since it contains an alkyl-benzene which represents an important chemical class present in diesel fuels. Experiments and numerical simulations have been performed on lift-off length and ignition delay in a wide range of conditions for a single-hole injector from ECN. The experiments were carried out in a constant-pressure flow facility able of reproducing engine-like thermodynamic conditions. The experiments focused in characterizing the ignition delay through the Schlieren technique, and the lift-off length through OH ∗ chemiluminescence visualization, at ECN suggested test conditions. On the other hand, computational fluid dynamics (CFD) simulations were performed using a multi-flamelet representative interactive flamelet (mRIF) model by taking consideration of turbulence–chemistry-interaction (TCI) with a beta-function on the form of scalar probability density functions (PDFs). This model is evaluated extensively over a wider range of parametric variations in this study. Encouraging results were obtained compared to the experiments with regards to the predictions of ignition delay and lift-off length at different ambient temperatures, ambient densities and fuel-injection pressures. Under predictions were found at less reactive conditions, which leave room for improvement in the future. [ABSTRACT FROM AUTHOR]

Highlights: [•] Three ECN nominal identical injectors show differences in spray penetration. [•] The injector opening causes differences in the instantaneous spray penetration. [•] The gas composition affect spray penetration rate and spreading angle. [•] Increasing the temperature (at constant density) has no effect on spray penetration. [•] An analysis with gas jet theory has been performed to reproduce the results obtained. [Copyright &y& Elsevier]

This work describes an experimental setup for obtaining pressure variation and rate of injection profiles per engine stroke. This study focuses on the following experimental parameters: flow meter's backpressure, injection pressure, and duration of the process. An IAV EVI-2-type flow meter is used to measure the rate of injection. The work has been carried out using a common rail system with a solenoid-operated injector. As result, time proÆ les of: current intensity throughout the injector (electric pulse), pressure variation in flow meter (p) and the rate of injection are presented. The study has been carried out with four different fuels: a diesel fuel without biodiesel, a diesel fuel with 5.83% of biodiesel, a biodiesel fuel derived from animal fats and a synthetic diesel fuel derived from a Fischer Tropsch process at low temperature. The experimental set up and the established procedures have proven to be adequate for studies with current diesel injection systems. The differences registered in rate of injection have been mainly caused by the differences in density of fuels studied.