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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.

The effects of spray targeting on mixing, combustion, and pollutant formation under a low-load, late-injection, low-temperature combustion (LTC) diesel operating condition are investigated by optical engine measurements and multi-dimensional modeling. Three common spray-targeting strategies are examined: conventional piston-bowl-wall targeting (152° included angle); narrow-angle floor targeting (124° included angle); and wide-angle piston-bowl-lip targeting (160° included angle). Planar laser-induced fluorescence diagnostics in a heavy-duty direct-injection optical diesel engine provide two-dimensional images of fuel-vapor, low-temperature ignition (H2CO), high-temperature ignition (OH) and soot-formation species (PAH) to characterize the LTC combustion process.

This paper presents a computational framework for the physics-based simulation of light vehicles operating on discrete terrain. The focus is on characterizing through simulation the mobility of vehicles that weigh 1000 pounds or less, such as a reconnaissance robot. The terrain is considered to be deformable and is represented as a collection of bodies of spherical shape. The modeling stage relies on a novel formulation of the frictional contact problem that requires at each time step of the numerical simulation the solution of an optimization problem. The proposed computational framework, when run on ubiquitous Graphics Processing Unit (GPU) cards, allows the simulation of systems in which the terrain is represented by more than 0.5 million bodies leading to problems with more than one million degrees of freedom.

Low-temperature combustion (LTC) strategies for diesel engines are of increasing interest because of their potential to significantly reduce particulate matter (PM) and nitrogen oxide (NOx) emissions. LTC with late fuel injection further offers the benefit of combustion phasing control because ignition is closely coupled to the fuel injection event. But with a short ignition-delay, fuel jet mixing processes must be rapid to achieve adequate premixing before ignition. In the current study, mixing and pollutant formation of late-injection LTC are studied in a single-cylinder, direct-injection, optically accessible heavy-duty diesel engine using three laser-based imaging diagnostics. Simultaneous planar laser-induced fluorescence of the hydroxyl radical (OH) and combined formaldehyde (H2CO) and polycyclic aromatic hydrocarbons (PAH) are compared with vapor-fuel concentration measurements from a non-combusting condition.

Heat transfer in internal combustion engines is taking on greater importance as manufacturers strive to increase efficiency while keeping pollutant emissions low and maintaining adequate performance. Wall heat transfer is experimentally evaluated using temperature measurements both on and below the surface using a physical model of conduction in the wall. Three classes of model inversion are used to recover heat flux from surface temperature measurements: analytical methods, numerical methods and inverse heat conduction methods; the latter method has not been previously applied to engine data. This paper details the inherent assumptions behind, required steps for implementation of, and merits and weaknesses of these heat flux calculation methods. The analytical methods, which have been most commonly employed for engine data, are shown to suffer from sensitivity to measurement noise that requires a priori signal filtering.

Prior HCCI optical engine experiments utilizing laser-induced fluorescence (LIF) measurements of stratified fuel-air mixtures have demonstrated the utility of probability density function (PDF) statistics for correlating mixture preparation with combustion. However, PDF statistics neglect all spatial details of in-cylinder fuel distribution. The current computational paper examines the effects of spatial fuel distribution on combustion using a novel combination of a 3-D CFD model with a 1-D linear-eddy model of turbulent mixing. In the simulations, the spatial coarseness of initial fuel distribution prior to the start of heat release is varied while keeping PDF statistics constant. Several cases are run, and as the initial mixture is made coarser, combustion phasing monotonically advances due to high local equivalence ratios that persist longer. The effect of turbulent mixing is more complex.

The mixing between the flows introduced through different intake valves of a four-valve engine was investigated optically. Each valve was fed from a different intake system, and the relative sensitivity to different flow parameters (manipulated with the goal of enhancing the bulk in-cylinder stratification) was investigated. Flow manipulation was achieved in three primary ways: modifying the intake runner geometry upstream of the head, introducing flow-directing baffles into the intake port, and attaching flow break-down screens to the intake valves. The relative merits of each flow manipulation method was evaluated using planar laser-induced fluorescence (PLIF) of 3-pentanone, which was introduced to the engine through only one intake valve. Images were acquired from 315° bTDC through 45° bTDC, and the level of in-cylinder stratification was evaluated on an ensemble and cycle-to-cycle basis using a novel column-based probability distribution function (PDF) contour plot.

A foundation of battery normalizations, modeling and control techniques is presented for charge sustaining HEV applications. Charge and voltage based battery state observers and controllers are compared. The voltage based technique is shown to provide robust state control, as it directly constrains terminal voltage. Additionally, it provides good power cycle efficiency, and is insensitive to the initialization and drift problems characteristic of charge based controllers. Special attention is given to VRLA batteries, and dynamic loads from typical driving cycles. Future work is introduced which identifies battery power capability and efficiency as possible state control variables. This work was supported by a Netherland-America Foundation Fellowship, and by the staff at the Technical University of Eindhoven, the Netherlands.

A commercial CFD package was used to develop a three-dimensional, fully turbulent model of the compressible flow across a complex-geometry venturi, such as those typically found in small engine carburetors. The results of the CFD simulations were used to understand the effect of the different obstacles in the flow on the overall discharge coefficient and the static pressure at the tip of the fuel tube. It was found that the obstacles located at the converging nozzle of the venturi do not cause significant pressure losses, while those obstacles that create wakes in the flow, such as the fuel tube and throttle plate, are responsible for most of the pressure losses. This result indicated that an overall discharge coefficient can be used to correct the mass flow rate, while a localized correction factor can be determined from three-dimensional CFD simulations in order to calculate the static pressure at locations of interest within the venturi.

A computational study was performed to evaluate the effects of bowl geometry, fuel spray targeting and swirl ratio under highly diluted, low-temperature combustion conditions in a heavy-duty diesel engine. This study is used to examine aspects of low-temperature combustion that are affected by mixing processes and offers insight into the effect these processes have on emissions formation and oxidation. The foundation for this exploratory study stems from a large data set which was generated using a genetic algorithm optimization methodology. The main results suggest that an optimal combination of spray targeting, swirl ratio and bowl geometry exist to simultaneously minimize emissions formation and improve soot and CO oxidation rates. Spray targeting was found to have a significant impact on the emissions and fuel consumption performance, and was furthermore found to be the most influential design parameter explored in this study.

Stoichiometric combustion could enable a three-way catalyst to be used for treating NOx emissions of diesel engines, which is one of the most difficult species for diesel engines to meet future emission regulations. Previous study by Lee et al. [1] showed that diesel engines can operate with stoichiometric combustion successfully with only a minor impact on fuel consumption. Low NOx emission levels were another advantage of stoichiometric operation according to that study. In this study, the characteristics of stoichiometric diesel combustion were evaluated experimentally to improve fuel economy as well as exhaust emissions The effects of fuel injection pressure, boost pressure, swirl, intake air temperature, combustion regime (injection timing), and engine load (fuel mass injected) were assessed under stoichiometric conditions.

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.

Simulations of DI Diesel engine combustion have been performed using a modified KIVA-II package with a recently developed phenomenological soot model. The phenomenological soot model includes generic description of fuel pyrolysis, soot particle inception, coagulation, and surface growth and oxidation. The computational results are compared with experimental data from a Cummins N14 single cylinder test engine. Results of the simulations show acceptable agreement with experimental data in terms of cylinder pressure, rate of heat release, and engine-out NOx and soot emissions for a range of fuel injection timings considered. The numerical results are also post-processed to obtain time-resolved soot radiation intensity and compared with the experimental data analyzed using two-color optical pyrometry. The temperature magnitude and KL trends show favorable agreement.

The introduction of high-pressure injection systems in D.I. diesel engines has highlighted already known drawbacks of in-cylinder turbulence modeling. In particular, the well known equilibrium hypothesis is far from being valid even during the compression stroke and moreover during the spray injection and combustion processes when turbulence energy transfer between scales occurs under non-equilibrium conditions. The present paper focuses on modeling in-cylinder engine turbulent flows. Turbulence is accounted for by using the RNG k-ε model which is based on equilibrium turbulence assumptions. By using a modified version of the Kiva-3 code, different mathematically based corrections to the computed macro length scale are proposed in order to account for non-equilibrium effects. These new approaches are applied to a simulation of a recent generation HSDI Diesel engine at both full load and partial load conditions representative of the emission EUDC cycle.

A method of determining the total hemispherical in-cylinder radiant heat transfer of a direct injection diesel engine was developed using the Two Color theory. A radiant probe was installed in the head of a single cylinder test engine version of a Cummins N14 diesel engine to facilitate the optical measurement. Two probes, installed one at a time, were used to provide the data to calculate the hemispherical radiant heat flux. Each of the probes had a different field of view but both had a near-hemispherical field of view and used a window material that exhibits a cosine-normalized response. The radiant probes were designed to be self-cleaning and remained free of soot deposits during engine operation at high load. The test engine was operated at 1200 and 1500 RPM and at 50, 75, and 100% load for each engine speed. At each operating combination of engine speed and load, measurements were made at several injection timings.

A new dynamometer system has been developed to improve the accuracy of tests that are run with a single cylinder version of a multi-cylinder engine. The dynamometer control system calculates the inertial torque and combustion torque that would normally be generated in a multi-cylinder engine. The system then applies the torque from the missing cylinders of the engine with the dynamometer. A unique high bandwidth hydraulic system is utilized to accurately apply these torque pulses. This allows the single-cylinder engine to have the identical instantaneous speed trajectory as the multi-cylinder engine, to test the single-cylinder engine at all engine speeds including very low speed operation, and to now do transient speed and load testing. Not only will this dramatically extend the capabilities of current single-cylinder engine test systems, but may open up new areas of research due to its transient testing capabilities.

A multidimensional simulation of Auxiliary Gas Injection (AGI) for late cycle oxygen enrichment was exercised to assess the merits of AGI for reducing the emissions of soot from heavy duty diesel engines while not adversely affecting the NOx emissions of the engine. Here, AGI is the controlled enhancement of mixing within the diesel engine combustion chamber by high speed jets of air or another gas. The engine simulated was a Caterpillar 3401 engine. For a particular operating condition of this engine, the simulated soot emissions of the engine were reduced by 80% while not significantly affecting the engine-out NOx emissions compared to the engine operating without AGI. The effects of AGI duration, timing, and orientation are studied to confirm the window of opportunity for realizing lower engine-out soot while not increasing engine out NOx through controlled enhancement of in-cylinder mixing.

The role of the fluid motion in a diesel engine on mixing and combustion was investigated using the CFD code Kiva-3v. The study considered pre-mixed charge compression ignition (PCCI) combustion that is a hybrid combustion system characterized by early injection timings and high amounts of EGR dilution to delay the start and lower the temperature of combustion. The fuel oxidizer mixture is not homogeneous at the start of combustion and therefore requires further mixing for complete combustion. PCCI combustion systems are characterized by relatively high CO and UHC emissions. This work investigates attenuating CO emissions by enhancing mixing processes through non-uniform flowfield motions. The fluid motion was characterized by the amount of average angular rotation about the cylindrical axis (swirl ratio) and the amount of non-uniform motion imparted by the relative amounts of mass inducted through tangential and helical intake ports in a 0.5L HSDI diesel engine.

This paper discusses the development of a novel deformable terrain database and its use in a co-simulation environment with a multibody dynamics vehicle model. The implementation of the model includes a general tire-terrain traction model which is modular to allow for any type of tire model that supports the Standard Tire Interface[1] to operate on the terrain. This allows arbitrarily complex tire geometry to be used, which typically has a large impact on the mobility performance of vehicles operating on deformable terrains. However, this gain in generality comes at the cost that popular analytical pressure-sinkage terramechanics models cannot be used to find the normal pressure and shear stress of the contact patch. Pressure and shear stress are approximated by combining the contributions from tire normal forces, shear stresses and bulldozing forces due to soil rutting.