The optimization of a modern direct injection diesel engine in terms of fuel consumption, power and pollutant emission requires an accurate study of the dynamic of the injection system for delivering, cycle to cycle, the right fuel quantity on the whole range of operative conditions. This paper reports the results of an experimental and numerical investigation on the stability of delivered amount of fuel in pilot injections supplied by a common rail system for heavy duty engines. The study aims to evaluate the performances in terms of fuel mass stability and cycle to cycle dispersion for short duration of energizing currents. Tests have been taken using an 8 holes, 0.21 mm diameter, 154° spray angle, having a flow rate of 1100 cm3/30 sec@10 MPa. Two different Programmable Electronic Control Units (a commercial and a home-made type), able to set different multinjection strategies, have been used to evaluate the performances of the system. Experiments have been focused on the analysis of the instantaneous flow rate and the fuel spray morphology both under non evaporative conditions and evaporative ones with the presence of a swirl motion. The fuel injection rate profiles for the implemented strategies have been measured by an AVL Injection Rate Gauge System working on the Bosch tube principle with time resolution up to 7.6 ¼s. Under non evaporative conditions, the spray evolution has been analyzed injecting the fuel in a quiescent high-pressure optically-accessible cylindrical vessel at different gas densities. Under evaporative conditions, the experiments have been carried out on a crank-case scavenged single-cylinder 2-stroke direct injection Diesel engine equipped with an optically accessible swirled combustion chamber. The engine is suitable to stabilize, during the compression stroke, a well structured swirl flow typical of real heavy duty engines. Images of the spray evolution, in single-shot mode, have been captured by a high resolution CCD camera, synchronized with the fuel emerging from the nozzle at different instant from the start of injection. They have been off-line processed by professional software to estimate the spray tip penetration and cone angle. A numerical investigation has been carried out by using the 3-D Star-CD code with the k-µ turbulence model, Huh-Gosman atomization model and Reitz-Diwaker secondary break-up model adopted to predict the fuel spray evolution within the prototype single cylinder 2-stroke Diesel. The grid of the engine has been made using STAR-CD tools and the experimental results have been used to give the initial conditions as well for the comparison of the prediction of the air velocity field and spray penetration within the combustion chamber. The initial pressure and temperature conditions have been imposed according to experimental data whereas the flow field distribution within the combustion chamber has been tested by comparison with the PIV results Images of the spray evolution, in single-shot mode, have been captured by a high resolution CCD camera, synchronized with the fuel emerging from the nozzle at different instant from the start of injection. They have been off-line processed by professional software to estimate the spray tip penetration and cone angle. A numerical investigation has been carried out by using the 3-D Star-CD code with the k-? turbulence model, Huh-Gosman atomization model and Reitz-Diwaker secondary break-up model adopted to predict the fuel spray evolution within the prototype single cylinder 2-stroke Diesel. The grid of the engine has been made using STAR-CD tools and the experimental results have been used to give the initial conditions as well for the comparison of the prediction of the air velocity field and spray penetration within the combustion chamber. The initial pressure and temperature conditions have been imposed according to experimental data whereas the flow field distribution within the combustion chamber has been tested by comparison with the PIV results.
Performances analysis of a common rail injection system for heavy duty diesel engines
Alfuso S;Allocca L;Auriemma M;Montanaro A;Valentino G
2008
Abstract
The optimization of a modern direct injection diesel engine in terms of fuel consumption, power and pollutant emission requires an accurate study of the dynamic of the injection system for delivering, cycle to cycle, the right fuel quantity on the whole range of operative conditions. This paper reports the results of an experimental and numerical investigation on the stability of delivered amount of fuel in pilot injections supplied by a common rail system for heavy duty engines. The study aims to evaluate the performances in terms of fuel mass stability and cycle to cycle dispersion for short duration of energizing currents. Tests have been taken using an 8 holes, 0.21 mm diameter, 154° spray angle, having a flow rate of 1100 cm3/30 sec@10 MPa. Two different Programmable Electronic Control Units (a commercial and a home-made type), able to set different multinjection strategies, have been used to evaluate the performances of the system. Experiments have been focused on the analysis of the instantaneous flow rate and the fuel spray morphology both under non evaporative conditions and evaporative ones with the presence of a swirl motion. The fuel injection rate profiles for the implemented strategies have been measured by an AVL Injection Rate Gauge System working on the Bosch tube principle with time resolution up to 7.6 ¼s. Under non evaporative conditions, the spray evolution has been analyzed injecting the fuel in a quiescent high-pressure optically-accessible cylindrical vessel at different gas densities. Under evaporative conditions, the experiments have been carried out on a crank-case scavenged single-cylinder 2-stroke direct injection Diesel engine equipped with an optically accessible swirled combustion chamber. The engine is suitable to stabilize, during the compression stroke, a well structured swirl flow typical of real heavy duty engines. Images of the spray evolution, in single-shot mode, have been captured by a high resolution CCD camera, synchronized with the fuel emerging from the nozzle at different instant from the start of injection. They have been off-line processed by professional software to estimate the spray tip penetration and cone angle. A numerical investigation has been carried out by using the 3-D Star-CD code with the k-µ turbulence model, Huh-Gosman atomization model and Reitz-Diwaker secondary break-up model adopted to predict the fuel spray evolution within the prototype single cylinder 2-stroke Diesel. The grid of the engine has been made using STAR-CD tools and the experimental results have been used to give the initial conditions as well for the comparison of the prediction of the air velocity field and spray penetration within the combustion chamber. The initial pressure and temperature conditions have been imposed according to experimental data whereas the flow field distribution within the combustion chamber has been tested by comparison with the PIV results Images of the spray evolution, in single-shot mode, have been captured by a high resolution CCD camera, synchronized with the fuel emerging from the nozzle at different instant from the start of injection. They have been off-line processed by professional software to estimate the spray tip penetration and cone angle. A numerical investigation has been carried out by using the 3-D Star-CD code with the k-? turbulence model, Huh-Gosman atomization model and Reitz-Diwaker secondary break-up model adopted to predict the fuel spray evolution within the prototype single cylinder 2-stroke Diesel. The grid of the engine has been made using STAR-CD tools and the experimental results have been used to give the initial conditions as well for the comparison of the prediction of the air velocity field and spray penetration within the combustion chamber. The initial pressure and temperature conditions have been imposed according to experimental data whereas the flow field distribution within the combustion chamber has been tested by comparison with the PIV results.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
