Search Results

In the current work, a series-hybrid vehicle has been constructed that utilizes a dual-fuel, Reactivity Controlled Compression Ignition (RCCI) engine. The vehicle is a 2009 Saturn Vue chassis and a 1.9L turbo-diesel engine converted to operate with low temperature RCCI combustion. The engine is coupled to a 90 kW AC motor, acting as an electrical generator to charge a 14.1 kW-hr lithium-ion traction battery pack, which powers the rear wheels by a 75 kW drive motor. Full vehicle testing was conducted on chassis dynamometers at the Vehicle Emissions Research Laboratory at Ford Motor Company and at the Vehicle Research Laboratory at Oak Ridge National Laboratory. For this work, the US Environmental Protection Agency Highway Fuel Economy Test was performed using commercially available gasoline and ultra-low sulfur diesel. Fuel economy and emissions data were recorded over the specified test cycle and calculated based on the fuel properties and the high-voltage battery energy usage.

In-cylinder blending of gasoline and diesel to achieve Reactivity Controlled Compression Ignition (RCCI) has been shown to reduce NOX and particulate matter (PM) emissions while maintaining or improving brake thermal efficiency as compared to conventional diesel combustion (CDC). The RCCI concept has an advantage over many advanced combustion strategies in that the fuel reactivity can be tailored to the engine speed and load allowing stable low-temperature combustion to be extended over more of the light-duty drive cycle load range. Varying the premixed gasoline fraction changes the fuel reactivity stratification in the cylinder providing further control of combustion phasing and pressure rise rate than the use of EGR alone. This added control over the combustion process has been shown to allow rapid engine operating point exploration without direct modeling guidance.

Advanced combustion systems that simultaneously address PM and NOx while retaining the high efficiency of modern diesel engines, are being developed around the globe. One of the most difficult problems in the area of advanced combustion technology development is the control of combustion initiation and retaining power density. During the past several years, significant progress has been accomplished in reducing emissions of NOx and PM through strategies such as LTC/HCCI/PCCI/PPCI and other advanced combustion processes; however control of ignition and improving power density has suffered to some degree - advanced combustion engines tend to be limited to the 10 bar BMEP range and under. Experimental investigations have been carried out on a light-duty DI multi-cylinder diesel automotive engine. The engine is operated in low temperature combustion (LTC) mode using 93 RON (Research Octane Number) and 74 RON fuel.

In a recent experimental study the in-cylinder spatial distribution of mixture equivalence ratio was quantified under non-combusting conditions by planar laser-induced fluorescence (PLIF) of a fuel tracer (toluene). The measurements were made in a single-cylinder, direct-injection, light-duty diesel engine at conditions matched to an early-injection low-temperature combustion mode. A fuel amount corresponding to a low load (3.0 bar indicated mean effective pressure) operating condition was introduced with a single injection at -23.6° ATDC. The data were acquired during the mixture preparation period from near the start of injection (-22.5° ATDC) until the crank angle where the start of high-temperature heat release normally occurs (-5° ATDC). In the present study the measured in-cylinder images are compared with a fully resolved three-dimensional CFD model, namely KIVA3V-RANS simulations.

Premixed charge compression ignition (PCI) strategies offer the potential for simultaneously low NOx and soot emissions with diesel-like efficiency. However, these strategies are generally confined to low loads due to inadequate control of combustion phasing and heat-release rate. One PCI strategy, dual-fuel reactivity-controlled compression ignition (RCCI), has been developed to control combustion phasing and rate of heat release. The RCCI concept uses in-cylinder blending of two fuels with different auto-ignition characteristics to achieve controlled high-efficiency clean combustion. This study explores fuel reactivity stratification as a method to control the rate of heat release for PCI combustion. To introduce fuel reactivity stratification, the research engine is equipped with two fuel systems. A low-pressure (100 bar) gasoline direct injector (GDI) delivers iso-octane, and a higher-pressure (600 bar) common-rail diesel direct-injector delivers n-heptane.

RNG k-ε closure turbulence dissipation equations are evaluated employing the CFD code KIVA-3V Release 2. The numerical evaluations start by considering simple jet flows, including incompressible air jets and compressible helium jets. The results show that the RNG closure turbulence model predicts lower jet tip penetration than the "standard" k-ε model, as well as being lower than experimental data. The reason is found to be that the turbulence kinetic energy is dissipated too slowly in the downstream region near the jet nozzle exit. In this case, the over-predicted R term in RNG model becomes a sink of dissipation in the ε-equation. As a second step, the RNG turbulence closure dissipation models are further tested in complex engine flows to compare against the measured evolution of turbulence kinetic energy, and an estimate of its dissipation rate, during both the compression and expansion processes.

The goal of this research is to investigate the physical parameters of stoichiometric operation of a diesel engine under a light load operating condition (6∼7 bar IMEP). This paper focuses on improving the fuel efficiency of stoichiometric operation, for which a fuel consumption penalty relative to standard diesel combustion was found to be 7% from a previous study. The objective is to keep NOx and soot emissions at reasonable levels such that a 3-way catalyst and DPF can be used in an aftertreatment combination to meet 2010 emissions regulation. The effects of intake conditions and the use of group-hole injector nozzles (GHN) on fuel consumption of stoichiometric diesel operation were investigated. Throttled intake conditions exhibited about a 30% fuel penalty compared to the best fuel economy case of high boost/EGR intake conditions. The higher CO emissions of throttled intake cases lead to the poor fuel economy.

A three-dimensional homogeneous equilibrium model (HEM) has been developed and implemented into an engine computational fluid dynamics (CFD) code KIVA-3V. The model was applied to simulate cavitating flow within injector nozzle passages. The effects of nozzle passage geometry and injection conditions on the development of cavitation zones and the nozzle discharge coefficient were investigated. Specifically, the effects of nozzle length (L/D ratio), nozzle inlet radius (R/D ratio) and K or KS factor (nozzle passage convergence) were simulated, and the effects of injection and chamber pressures, and time-varying injection pressure were also investigated. These effects are well captured by the nozzle flow model, and the predicted trends are consistent with those from experimental observations and theoretical analyses.

Engine development is both time consuming and economically straining. Therefore, efforts are being made to optimize the research and development process for new engine technologies. The ability to apply information gained by studying an engine of one size/application to an engine of a completely different size/application would offer savings in both time and money in engine development. In this work, a computational study of diesel engine size-scaling relationships was performed to explore engine scaling parameters and the fundamental engine operating components that should be included in valid scaling arguments. Two scaling arguments were derived and tested: a simple, equal spray penetration scaling model and an extended, equal lift-off length scaling model. The simple scaling model is based on an equation for the conservation of mass and an equation for spray tip penetration developed by Hiroyasu et al. [1].

High-speed video imaging in a swirl-supported (Rs = 1.7), direct-injection heavy-duty diesel engine operated with moderate-to-high EGR rates reveals a distinct correlation between the spatial distribution of luminous soot and mean flow vorticity in the horizontal plane. The temporal behavior of the experimental images, as well as the results of multi-dimensional numerical simulations, show that this soot-vorticity correlation is caused by the presence of a greater amount of soot on the windward side of the jet. The simulations indicate that while flow swirl can influence pre-ignition mixing processes as well as post-combustion soot oxidation processes, interactions between the swirl and the heat release can also influence mixing processes. Without swirl, combustion-generated gas flows influence mixing on both sides of the jet equally. In the presence of swirl, the heat release occurs on the leeward side of the fuel sprays.

Engine-out CO emission and fuel conversion efficiency were measured in a highly-dilute, low-temperature diesel combustion regime over a swirl ratio range of 1.44-7.12 and a wide range of injection timing. At fixed injection timing, an optimal swirl ratio for minimum CO emission and fuel consumption was found. At fixed swirl ratio, CO emission and fuel consumption generally decreased as injection timing was advanced. Moreover, a sudden decrease in CO emission was observed at early injection timings. Multi-dimensional numerical simulations, pressure-based measurements of ignition delay and apparent heat release, estimates of peak flame temperature, imaging of natural combustion luminosity and spray/wall interactions, and Laser Doppler Velocimeter (LDV) measurements of in-cylinder turbulence levels are employed to clarify the sources of the observed behavior.

Although in-cylinder optical diagnostics have provided significant understanding of conventional diesel combustion, most alternative combustion strategies have not yet been explored to the same extent. In an effort to build the knowledge base for alternative low-temperature combustion strategies, this paper presents a comparison of three alternative low-temperature combustion strategies to two high-temperature conventional diesel combustion conditions. The baseline conditions, representative of conventional high-temperature diesel combustion, have either a short or a long ignition delay. The other three conditions are representative of some alternative combustion strategies, employing significant charge-gas dilution along with either early or late fuel injection, or a combination of both (double-injection).

Managing the injection rate profile is a powerful tool to control engine performance and emission levels. In particular, Common Rail (C.R.) injection systems allow an almost completely flexible fuel injection event in DI-diesel engines by permitting a free mapping of the start of injection, injection pressure, rate of injection and, in the near future, multiple injections. This research deals with the development of a network-based numerical tool for understanding operating condition limits of the Common Rail injector. The models simulate the electro-fluid-mechanical behavior of the injector accounting for cavitation in the nozzle holes. Validation against experiments has been performed. The model has been used to provide insight into the operating conditions of the injector and in order to highlight the application to injection system design.

Fuel Injection System (FIS) research on injection pressure, timing control, and rate shaping, and studies on the modeling of injector nozzle flows and their effect on fuel spray characteristics are usually conducted separately. Only recently has the fuel injection and spraying process been studied as a complete system, i.e., including both the high-pressure fuel delivery and its effect on the nozzle flow characteristics, including nozzle cavitation. A methodology for coupling the fuel injection system and its effect on spray characteristics is presented here. The method is applied to an example case of a conventional pump-line-nozzle system. Mathematical models for characterizing the flows from the pump to the nozzle are formulated and solved using the Method of Characteristics and finite difference techniques. The nozzle internal flow is modeled using zero-dimensional flow models, in which the nozzle cavitation and its effect on the nozzle exit flow are accounted for.

Intake flow simulations were carried out for a prototype DISI engine using the standard k-ε model and the RNG k-ε model. The results were compared with PTV (transient water analog) measurements. The study was focused on low load operations with engine speed at 400 rev/min. Two cases were studied, a single intake case in which one intake port was blocked and a dual intake port case. In the computations, the results show that the standard k-ε model tends to produce higher turbulence levels when turbulence is generated and decays faster when turbulence dissipates. Different turbulence models predict almost the same flow structures. However, the effects of the turbulence model on the predicted tumble and swirl ratios are significant. The TKE distributions at BDC predicted by the two models are also different. The standard k-ε model seems to be more diffusive. Good agreements with PTV data were obtained in the single valve case with the RNG k-ε model.

Various single and split injection schemes are studied to provide a better understanding of fuel distribution during cold starting in DI diesel engines. Improved spray-wall interaction, fuel film and multicomponent vaporization models are used to analyze the combustion processes. Better combustion characteristics are obtained for the split injection schemes than with a single injection. An analysis of the fuel impingement processes identifies the mechanisms involved in producing the differences in vaporization and combustion of the fuel. A greater amount of splashing occurred for the split injections compared to a single injection. This behavior is attributed to the decreased film thickness (less dissipation of impingement energy), the decreased impingement area (obtained by increasing the impingement Weber number), and most importantly, the reduced frequency of drop impingement.

Two-Color imaging optics were developed and used to observe soot emission processes in a modern heavy-duty diesel engine. The engine was equipped with a common rail, electronically-controlled, high-pressure fuel injection system that is capable of up to four injection pulses per engine cycle. The engine was instrumented with an endoscope system for optical access for the combustion visualization. Multidimensional combustion and soot modeling results were used for comparisons to enhance the understanding and interpretation of the experimental data. Good agreement between computed and measured cylinder pressures, heat release and soot and NOx emissions was achieved. In addition, good qualitative agreement was found between in-cylinder soot concentration (KL) and temperature fields obtained from the endoscope images and those obtained from the multidimensional modeling.

Fuel spray atomization and breakup processes within a direct-injection spark-ignition (DISI) engine and outside the engine were modeled using a modified KIVA-3V code with improved spray models. The structures of the predicted sprays were qualitatively compared with planar images. The considered sprays were created by a prototype pressure-swirl injector and the planar images were obtained by laser sheet imaging in an optical DISI engine. In the out-of-engine case, the spray was injected into atmospheric air, and was modeled in a two dimensional bomb. In the engine case, the injection started from 270° ATDC, and full 3-D computations in the same engine were performed. In both cases, two liquid injection pressure conditions were applied, that is, 3.40 MPa and 6.12 MPa. The model gives good prediction of the tip penetration, and external spray shape, but the internal structure prediction has relatively lower accuracy, especially near the spray axis.

Liquid fuel penetration was measured using an endoscopebased imaging system in an operating single-cylinder heavy-duty direct injection diesel engine with simulated turbocharging. Sprays were imaged via the elastic backscatter technique without significantly altering the engine geometry. Light loads (or pilot injections) were also studied because the spray breakup, mixing and vaporization processes can be isolated since they are less influenced by heat feedback from the flame than in a full injection case. The pilot injections included cases with three different fuel amounts (10%, 15% and 20% of the fuel injected in the baseline case, i.e., 75% load and 1600 rev/min) with different start-of-injection timings. Maximum liquid penetration lengths beyond which the fuel is completely vaporized were observed for all the cases studied. The maximum lengths varied from 23 mm to 28 mm for the different start-of-injection timings.

A study was performed to correlate the Sauter Mean Diameter (SMD), NOx and particulate emissions of a direct injection diesel engine with various injection pressures and different nozzle geometry. The spray experiments and engine emission tests were conducted in parallel using the same fuel injection system and same operating conditions. With high speed photography and digital image analysis, a light extinction technique was used to obtain the spray characteristics which included spray tip penetration length, spray angle, and overall average SMD for the entire spray. The NOx and particulate emissions were acquired by running the tests on a fully instrumented Caterpillar 3406 heavy duty engine. Experimental results showed that for higher injection pressures, a smaller SMD was observed, i.e. a finer spray was obtained. For this case, a higher NOx and lower particulate resulted.