Combining Instantaneous Temperature Measurements and CFD for Analysis of Fuel Impingement on the DISI Engine Piston Top

2010 ◽  
Vol 132 (7) ◽  
Author(s):  
Kukwon Cho ◽  
Ronald O. Grover ◽  
Dennis Assanis ◽  
Zoran Filipi ◽  
Gerald Szekely ◽  
...  
Keyword(s):  
Film Thickness ◽  
Heat Loss ◽  
Cfd Simulation ◽  
Computational Study ◽  
Direct Injection ◽  
Negative Temperature ◽  
Spark Ignition Engine ◽  
Fuel Injector ◽  
Fuel Film ◽  
Film Evaporation

A two-pronged experimental and computational study was conducted to explore the formation, transport, and vaporization of a wall film located at the piston surface within a four-valve, pent-roof, direct-injection spark-ignition engine, with the fuel injector located between the two intake valves. Negative temperature swings were observed at three piston locations during early injection, thus confirming the ability of fast-response thermocouples to capture the effects of impingement and heat loss associated with fuel film evaporation. Computational fluid dynamics (CFD) simulation results indicated that the fuel film evaporation process is extremely fast under conditions present during intake. Hence, the heat loss measured on the surface can be directly tied to the heating of the fuel film and its complete evaporation, with the wetted area estimated based on CFD predictions. This finding is critical for estimating the local fuel film thickness from measured heat loss. The simulated fuel film thickness and transport corroborated well temporally and spatially with measurements at thermocouple locations directly in the path of the spray, thus validating the spray and impingement models. Under the strategies tested, up to 23% of fuel injected impinges upon the piston and creates a fuel film with thickness of up to 1.2 μm. In summary, the study demonstrates the usefulness of heat flux measurements to quantitatively characterize the fuel film on the piston top and allows for validation of the CFD code.

Combining Instantaneous Temperature Measurements and CFD for Analysis of Fuel Impingement on the DISI Engine Piston Top

2009 ◽  
Author(s):  
Kukwon Cho ◽  
Ronald O. Grover ◽  
Dennis Assanis ◽  
Zoran Filipi ◽  
Gerald Szekely ◽  
...  
Keyword(s):  
Film Thickness ◽  
Heat Loss ◽  
Cfd Simulation ◽  
Computational Study ◽  
Fluid Dynamic ◽  
Direct Injection ◽  
Negative Temperature ◽  
Fuel Injector ◽  
Fuel Film ◽  
Film Evaporation

A two-pronged experimental and computational study was conducted to explore the formation, transport, and vaporization of a wall film located on the piston surface within a four-valve, pent roof, direct-injection spark-ignition (DISI) engine, with the fuel injector located between the two intake valves. Negative temperature swings were observed at three piston locations during early injection, thus confirming the ability of fast-response thermocouples to capture the effects of impingement and heat loss associated with fuel film evaporation. Computational Fluid Dynamic (CFD) simulation results demonstrated that the fuel film evaporation process is extremely fast under conditions present during intake. Hence, the heat loss measured on the surface can be directly tied to the heating of the fuel film and its complete evaporation, with the wetted area estimated based on CFD predictions. This finding is critical for estimating the local fuel film thickness from measured heat loss. The simulated fuel film thickness and transport corroborated well temporally and spatially with measurements at thermocouple locations directly in the path of the spray, thus validating the spray and impingement models. Under the strategies tested, up to 23% of fuel injected impinges upon the piston and creates a fuel film with thickness of up to 1.2 μm. In summary, the study demonstrates the usefulness of heat flux measurements to quantitatively characterize the fuel film on the piston top and allows for validation of the CFD code.

scholarly journals Effect of engine conditions and injection timing on piston-top fuel films for stratified direct-injection spark-ignition operation using E30

2019 ◽  
Vol 21 (2) ◽  
pp. 302-318 ◽  
Author(s):  
Carl-Philipp Ding ◽  
David Vuilleumier ◽  
Namho Kim ◽  
David L Reuss ◽  
Magnus Sjöberg ◽  
...  
Keyword(s):  
Refractive Index ◽  
Direct Injection ◽  
Spark Ignition ◽  
Spark Ignition Engine ◽  
Injection Timing ◽  
Fuel Film ◽  
Index Matching ◽  
Refractive Index Matching ◽  
Wall Wetting ◽  
Direct Injection Spark Ignition

Mid-level ethanol/gasoline blends can provide knock resistance benefits for stoichiometric spark-ignition engine operation, but previous studies have identified challenges associated with spray impingement and wall wetting, leading to excessive particulate matter emissions. At the same time, stratified-charge spark-ignition operation can provide increased thermal efficiency, but care has to be exercised to avoid excessive in-cylinder soot formation. In support of the use of mid-level ethanol/gasoline blends in advanced spark-ignition engines, this study presents spray and fuel-film measurements in a direct-injection spark-ignition engine operated with a 30 vol.%/70 vol.% ethanol/gasoline blend (E30). Crank-angle resolved fuel-film measurements at the piston surface are conducted using two different implementations of the refractive index matching technique. A small-angle refractive index matching implementation allows quantification of the wetted area, while a large-angle refractive index matching implementation enables semi-quantitative measurements of fuel-film thickness and volume, in addition to fuel-film area. The fuel-film measurements show that both the amount of fuel deposited on the piston and the shape of the fuel-film patterns are strongly influenced by the injection timing, duration, intake pressure, and coolant temperature. For combinations of high in-cylinder gas density and long injection duration, merging of the individual spray plumes, commonly referred to as spray collapse, can cause a dramatic change to the shape and thickness of the wall fuel films. Overall, the study provides guidance to engine designers aiming at minimizing wall wetting through tailored combinations of injection timings and durations.

Simulation of electrosprays in model direct-injection spark-ignition engine in-cylinder flows

2005 ◽  
Vol 6 (6) ◽  
pp. 527-546 ◽  
Author(s):  
G C S Nhumaio ◽  
A P Watkins
Keyword(s):  
Direct Injection ◽  
Axisymmetric Flow ◽  
Spark Ignition ◽  
Spark Ignition Engine ◽  
Cylinder Wall ◽  
Half Cycle ◽  
Fuel Film ◽  
Reference Case ◽  
Multiple Pulses ◽  
Direct Injection Spark Ignition

The calculated effects on injected charged sprays of dielectric and conductive in-cylinder wall materials are presented for a half-cycle of an axisymmetric flow model direct-injection spark-ignition (DISI) engine. A plain orifice electrostatic atomizer, previously used in experiments for application in fuel burners, is embodied into the EPISO code and this is assumed to pump a charged spray while working at moderate pressures of 5 MPa and fuel deliveries of 5 cm3/s, the maximum rates currently reported in electrostatic atomization of hydrocarbons. The transition mode operation of DISI engines is selected for the study and this consists of multiple pulses of 5 mg each, occurring at 80, 150, and 300° crank angle with the engine running at 3000 r/min. In the case of the third pulse, which impinges on the piston surface, the wall impaction model of Park and Watkins is used particularly when an electric potential of 1 kV is applied on this surface for it helps to reduce excessive fuel film build-up. Particles impinging on the cylinder roof and liner are treated with the stick impaction model of Naber and Reitz. A simple axisymmetric engine geometry of flat piston and cylinder heads is considered and computations of an uncharged spray are taken as a reference case. It is found in the study, firstly, that charge improves mixture preparation when dielectric in-cylinder surfaces are used, secondly, that the need for charge drainage in metallic surfaces produces poor spray characteristics in comparison with an ideal charged spray with boundary electric fields (this is shown by the large impingement of drop parcels relative to an ordinary spray as well as to a charged spray with electric boundary fields) and, thirdly, that charge reduces the fuel film thickness on the piston surface during late injection.

scholarly journals Experimental and Computational Study of n-Heptane Autoignition in a Direct-Injection Constant-Volume Combustion Chamber

2014 ◽  
Vol 136 (9) ◽  
Author(s):  
James C. Allen ◽  
William J. Pitz ◽  
Brian T. Fisher
Keyword(s):  
Combustion Chamber ◽  
Computational Study ◽  
Direct Injection ◽  
Negative Temperature ◽  
Constant Volume ◽  
Chamber Pressure ◽  
Combustion Model ◽  
Significant Finding ◽  
Constant Volume Combustion ◽  
Constant Volume Combustion Chamber

The purpose of this study was to characterize experimental n-heptane combustion behavior in a direct-injection constant-volume combustion chamber (DI-CVCC), using chamber pressure to infer ignition delay and heat-release rate. Measurements generally displayed expected trends and indicated entirely premixed combustion with no mixing-controlled phase. A significant finding was the observation of negative temperature coefficient (NTC) behavior. Comparing results with CHEMKIN-PRO simulations, it was found that a homogeneous combustion model was reasonably accurate for ignition delays longer than 5 ms. The combination of NTC behavior and homogeneous fuel-air mixtures suggests that this DI-CVCC can be useful for validation of chemical-kinetic mechanisms.

Analytical model for liquid film evaporation on fuel injector tip for the mitigation of injector tip wetting and the resulting particulate emissions in gasoline direct-injection engines

2020 ◽  
pp. 146808742097389
Author(s):  
Fahad M Alzahrani ◽  
Mohammad Fatouraie ◽  
Volker Sick
Keyword(s):  
Liquid Film ◽  
Analytical Model ◽  
Time Constant ◽  
Direct Injection ◽  
Operating Conditions ◽  
Gasoline Direct Injection ◽  
Particulate Emissions ◽  
Fuel Injector ◽  
Direct Injection Engines ◽  
Film Evaporation

Unevaporated fuel films forming on the fuel injector tip of gasoline direct-injection engines burn in a diffusion flame at the time of spark, producing particulates and at some operating conditions, these films have been identified as the dominating source of particulate emissions. This work developed an analytical model for liquid film evaporation on the injector tip, that is, injector tip drying, for the mitigation of injector tip wetting and the resulting particulate emissions. The model explains theoretically how fuel films on the injector tip evaporate with time from the end of injection to the spark. The model takes into consideration engine operating conditions, including engine load and speed, tip and fuel temperatures, gas temperature and pressure, and fuel properties. The model explains the observed trends in particulate number (PN) emissions due to injector tip wetting. Engine experiments were used to validate the model by correlating the predicted film mass at the time of spark to measurements of PN emissions at different conditions. A tip drying time constant was also defined and was found to correlate well with the measured PN for all conditions tested. This time constant is a deterministic factor for mitigating tip wetting. In general, the results indicate that the liquid film evaporation on the injector tip follows a first order, asymptotic behavior. Furthermore, the tip drying physics causes the observed increasing and decreasing non-linear trends in PN emissions with the engine load and the available time for tip drying, respectively. Additionally, the liquid film evaporation on the injector tip is highly sensitive to most of the injector initial and boundary conditions, including the initial film mass after the end of injection, the wetted surface area, the available time for tip drying and the injector tip temperature. The initial film temperature has the least effect on film mass evaporation.

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