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The US Army uses a light tactical High-Mobility Multi-Purpose Wheeled Vehicle (HMMWV) which, due to the amount of armor added, requires air conditioning to keep its occupants comfortable. The current system uses R134a in a dual evaporator, remote-mounted condenser, engine-driven compressor system. This vehicle has been adapted to use an environmentally friendly refrigerant (carbon dioxide) to provide performance, efficiency, comfort and logistical benefits to the Army. The unusual thermal heat management issues and the fact that the vehicle is required to operate under extreme ambient conditions have made the project extremely challenging. This paper is a continuation of work presented at the SAE Alternate Refrigerants Symposium held in Phoenix last June [1].

Combustion chamber deposits in spark ignition engines act as thermal insulators and can lead to octane requirement increase. The thermal properties of deposits are not well documented, the reported thermal diffusivity values vary by two orders of magnitude. Two thermal property measurement techniques were compared, the flash and steady illumination laser methods. The steady laser method was more suitable for deposit property measurement. A comparison was made of the thermal properties of deposits grown with a base fuel with the thermal properties of deposits grown with the base fuel doped with reformer bottoms. For the clean fuel the thermal diffusivity ranged from 3.5 to 3.9-7 m2/s, at various locations around the combustion chamber. For the fuel doped with reformer bottoms the thermal diffusivity ranged from 1.1 to 1.9-7 m2/s at different locations within the combustion chamber.

A geometrically accurate, three-dimensional finite element model of a Diesel engine exhaust valve and cylinder head assembly has been developed to analyze the effect of cylinder head interactions on exhaust valve stresses. Results indicate that a multi-lobed stress pattern occurs around the exhaust valve head due to cylinder head deformation, stiffness variations, and thermal asymmetry. Consequently, peak valve bending and hoop stresses from the three-dimensional model are 48% and 40% higher, respectively, than for the two-dimensional, axisymmetric model. These results indicate the degree of model complexity required for more accurate analyses of exhaust valve operating stresses.

This paper presents system identification methods of using both frequency and time domain analyses to estimate system parameters for a nonlinear electrohydraulic (E/H) tractor steering system. The frequency domain method identified parameters of the system using a linear model with a nonlinear gain function. The time domain method identified those parameters using a discrete time expression. A method of multiple models was used to represent the nonlinear system for both frequency and time domain analyses. Simulation and test results showed that the modified identification method could satisfactorily identify the parameters of the nonlinear E/H tractor steering system.

Biodiesel is a widely used biofuel in diesel engines, which is of particular interest as a renewable fuel because it possesses the similar properties as the diesel fuel. The pure soybean biodiesel was tested in an optical constant volume combustion chamber using natural flame luminosity and forward illumination light extinction (FILE) methods to explore the combustion process and soot distribution at various ambient temperatures (800 K and 1000 K) and oxygen concentrations (21%, 16%, 10.5%). Results indicated that, with a lower ambient temperature, the autoignition delay became longer for all three oxygen concentrations and more ambient air was entrained by spray jet and more fuel was burnt by premixed combustion. With less ambient oxygen concentration, the heat release rate showed not only a longer ignition delay but also longer combustion duration.

An optically accessible single-cylinder high-speed direct-injection (HSDI) Diesel engine equipped with a Bosch common rail injection system was used to study the spray and combustion processes for European low sulfur diesel, bio-diesel, and their blends at different blending ratio. Influences of injection timing and fuel type on liquid fuel evolution and combustion characteristics were investigated under similar loads. The in-cylinder pressure was measured and the heat release rate was calculated. High-speed Mie-scattering technique was employed to visualize the liquid distribution and evolution. High-speed combustion video was also captured for all the studied cases using the same frame rate. NOx emissions were measured in the exhaust pipe. The experimental results indicated that for all of the conditions the heat release rate was dominated by a premixed combustion pattern and the heat release rate peak became smaller with injection timing retardation for all test fuels.

The spray structure and vaporization processes of flash-boiling sprays in a constant volume chamber under a wide range of superheated conditions were experimentally investigated by a high speed imaging technique. The Engine Combustion Network’s Spray G injector was used. Four fuels including gasoline, ethanol, and gasoline-ethanol blends E30 and E50 were investigated. Spray penetration length and spray width were correlated to the degree of the superheated degree, which is the ratio of the ambient pressure to saturated vapor pressure (pa/ps). It is found that parameter pa/ps is critical in describing the spray transformation under flash-boiling conditions. Three distinct stages namely the slight flash-boiling, the transition flash-boiling, and the flare flash-boiling are identified to describe the transformation of spray structures.

Automotive software complexity has been growing rapidly with time. The demand for automation in automotive segment including autonomous automobiles and software based products has caught the attention of researchers. Hence, it is necessary to check the complexity of automotive software and their reliability growth. Testing in the field of software artifact is resource intensive exercise. If project managers are able to put forward testing activities well then the testing resource consumptions may be much more resource/cost efficient. Reliability can be estimated during testing phase of software using software reliability growth models (SRGMs). A software package Computer Aided Software Reliability Estimation (CASRE) has many important SRGMs. These SRGMs are based on Non-Homogeneous Poisson Process (NHPP), Markov process or Bayesian models.

Combustion processes employing different injection strategies in a High-Speed Direct Inject (HSDI) diesel engine were investigated using a narrow angle injector (70 degree). Whole-cycle combustion was visualized using a high-speed digital video camera. The liquid spray evolution process was imaged by the Mie-scattering technique. Different injection strategies were employed in this study including early pre-Top Dead Center (TDC) injection, post-TDC injection, multiple injection strategies with an early pre-TDC injection and a late post-TDC injection. Smokeless combustion was obtained under some operating conditions. Compared with the original injection angle (150 degree), some new combustion phenomena were observed for certain injection strategies. For early pre-TDC injection strategies, liquid fuel impingement is observed that results in some newly observed fuel film combustion flame (pool fires) following an HCCI-like weak flame.

Aircraft incidents and accidents in icing are often the result of degradation in performance and control. However, current ice sensors measure the amount of ice and not the effect on performance and control. No processed aircraft performance degradation information is available to the pilot. In this paper research is reported on a system to estimate aircraft performance and control changes due to ice, then use this information to automatically operate ice protection systems, provide aircraft envelope protection and, if icing is severe, adapt the flight controls. Key to such a safety system would be he proper communication to, and coordination with, the flight crew. This paper reviews the basic system concept, as well as the research conducted in three critical areas; aerodynamics and flight mechanics, aircraft control and identification, and human factors.

Bio-butanol has been widely investigated as a promising alternative fuel. However, the main issues preventing the industrial-scale production of butanol is its relatively low production efficiency and high cost of production. Acetone-butanol-ethanol (ABE), the intermediate product in the ABE fermentation process for producing bio-butanol, has attracted a lot of interest as an alternative fuel because it not only preserves the advantages of oxygenated fuels, but also lowers the cost of fuel recovery for individual component during fermentation. If ABE could be directly used for clean combustion, the separation costs would be eliminated which save an enormous amount of time and money in the production chain of bio-butanol.

Reductions of noise in vehicle passenger compartments in recent years have made some previously undetectable noises audible. Expansion devices used in automobile air conditioning systems are known producers of noise. The fact that these devices are mounted very close to the passengers increases the problems associated with the reduction of this noise. The understanding of the propagation mechanisms from the noise generated in the refrigerant by the expansion device, through the tube and evaporator walls, and finally to the outside air is important. This paper will focus on how noise from expansion devices is transmitted through tube walls downstream of the expansion valve.

This paper presents the study of refrigerant charge imbalance between A/C (cooling) mode and HP (heating) mode of a mobile reversible system. Sensitivities of cooling and heating capacity and energy efficiency with respect to refrigerant charge were investigated. Optimum refrigerant charge level for A/C mode was found to be larger than that for HP mode, primarily due to larger condenser size in A/C mode. Refrigerant charge retention in components at both modes were measured in the lab by quick close valve method. Modeling of charge retention in heat exchangers was compared to experimental measurements. Effect of charge imbalance on oil circulation was also discussed.

A normally aspirated, four-stroke diesel engine was tested under operation with two alcohol containing fuel blends. The fuels contained ethanol, butanol, heavy virgin distillate, diesel Nos. 2 and 4, and a cetane improver. The proportions of the components were selected to give blends with properties within the range of diesel No. 2. The final blends contained 25 and 43.7 percent alchohols. Test results showed a loss in power due to the reduced heating value of the blends, and some deterioration of performance at light loads. At intermediate to heavy loads, satisfactory performance was obtained.

The demand for mobile heat pump systems increases with the growing popularity of electric vehicles. One big challenge of such systems using low pressure refrigerant is the substantial drop of heating capacity at low ambient temperature conditions, when heat is most needed. The low suction density associated with low operating pressure in the evaporator is the major reason for the capacity drop. In extremely low ambient temperature, compressor speed may need to be regulated in order to prevent suction pressure going below atmospheric pressure, hence further reducing heat pumping capability. Other factors like pressure drop induced temperature glide and refrigerant maldistribution in the outdoor evaporator also weakens the system ability to absorb heat from ambient air. This paper presents detailed and in-depth analysis of the performance and limiting factors on low ambient temperature operation of a mobile heat pump system using refrigerant R1234yf.

Carbon dioxide (CO2 or R744) is a promising next-generation refrigerant for mobile air-conditioning applications (MAC), which has the advantages of good heating performance in cold climates and environmental-friendly properties. This paper presents a simulation model of an integrated internal heat exchanger (IHX) and accumulator (Acc) using the finite volume method. The results are validated by a group of experimental data collected with different transcritical R744 mobile air-conditioner and heat pump (MHP) systems, and the error was within ±10%. The impacts of refrigerant mass flow rate and operating temperatures on the heat transfer rate of the IHX, improvement on refrigeration capacity and the liquid level in the Acc were studied. Results show that the net benefits of IHX are significant in AC mode, while it helps preventing flooding of the compressor in MHP mode.

A numerical investigation of air-fuel mixing in gasoline direct-injection (GDI) engines is presented in this paper. The primary goal of this study is to demonstrate the importance of fuel representation. In the past studies, fuel has been usually modeled as a single component substance. However, most fuels are mixtures of hydrocarbons with diverse boiling points, resulting in mixture vaporization behavior substantially different from single-component behavior. This study presents a newly developed multicomponent vaporization model, which takes into account important mechanisms such as preferential vaporization, internal circulation, surface regression, and non-ideal behavior in high-pressure environments. A sheet spray atomization model was also used to calculate the disintegration of the liquid sheet and the breakup of the subsequent droplets. The results of a single-component fuel representation and a multicomponent fuel representation were compared.

An efficient multi-component fuel droplet vaporization model has been developed in this work using discrete approach. The precise modeling of droplet vaporization process is divided into two parts: vapor-phase and liquid-phase sub-models. Temporal evolution of flow inside the droplet is considered to describe the transient behavior introduced by the slow diffusion process. In order to account for the internal circulation motion, surface regression and finite diffusion without actually resolving the spatial governing equations within the liquid phase, a set of ordinary differential equations is applied to describe the evolution of the non-uniform distributions of universal diffusional variables, i.e. temperature and species mass fraction. The differences between the droplet surface and bulk mean states are modeled by constructing a quasi-1D frame; the effect of the internal circulations is taken into consideration by using the effective diffusivity rather than physical diffusivity.

This paper describes a numerical study on air/fuel preparation process in a direct-injected spark-ignition engine under partial load stratified conditions. The fuel is represented as a mixture of four components with a distillation curve similar to that of actual gasoline, and its vaporization processes are simulated by two recently formulated multicomponent vaporization models for droplet and film, respectively. The models include major mechanisms such as non-ideal behavior in high-pressure environments, preferential vaporization, internal circulation, surface regression, and finite diffusion in the liquid phase. A spray/wall impingement model with the effect of surface roughness is used to represent the interaction between the fuel spray and the solid wall. Computations of single droplet and film on a flat plate were first performed to study the impact of fuel representation and vaporization model on the droplet and film vaporization processes.

High costs and extreme risks prevent the life testing of NASA hardware. These unavoidable limitations prevent the determination of sound reliability bounds for NASA hardware; thus the true risk assumed in future missions is unclear. A simulation infrastructure for determining these risks is developed in a configurable format here. Positive preliminary results in preparation for validation testing are reported. A stochastic filter simulates non-deterministic output from the various unit processes. A maintenance and repair module has been implemented with several levels of complexity. Two life testing approaches have been proposed for use in future model validation.