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Co-Optimization of Fuels and Engines initiative (Co-Optima) of the U.S Department of Energy started investigations on several candidates of biofuels and blends for internal combustion engines. At this stage, only a few biomass-derived fuel blendstocks (including ethanol) for advanced spark-ignition engines have been selected using enhanced screening criteria, which included boiling point, toxicity, research octane number, octane sensitivity, and economical distribution system, etc. Ethanol, of which this paper is focused on, is also an important fuel because of its high-octane number which in turn promotes advance ignition timing and higher thermal efficiencies in reciprocating engines. Measurements of laminar burning velocity (LBV) is a key metric to understand fuel performance and applicability in engines. Furthermore, in order to quantify more complicated, and practical, burning regimes such as turbulent combustion much of the underlying theory requires knowledge of LBV.

This paper presents the concept of a dual latent heat sink for thermal management of pulse heat generating electronic systems. The focus of this work is to verify the effectiveness of the concept during charging through experimentation. Accordingly, custom components were built and a prototype version of the heat sink was fabricated. Experiments were performed to investigate the implementation feasibility and heat transfer performance. It is shown that this heat sink is practicable and helps in arresting the system temperature rise during charging (period of pulse heat load).

This paper reviews the literature which identifies the causes, consequences and cures for engine knock as it affects high performance engines. The physical events of normal and abnormal combustion are described. The observed variations in combustion phenomenon are explained through chemical kinetics. A mathematical model of combustion which can predict knock in an engine cylinder is summarized. Several mechanisms of knock induced damage are outlined. Design and operating considerations which affect an engine's propensity to knock are discussed. Terms that have become associated with combustion in general and the knocking phenomenon in particular are collected and examined

A power electronics module was equipped with an evaporative spray cooling nozzle assembly that served to remove waste heat from the silicon devices. The spray cooling nozzle assembly took the place of the standard heat sink, which uses single phase convection. The purpose of this work was to test the ability of spray cooling to enable higher power density in power electronics with high temperature coolant, and to be an effective and lightweight system level solution to the thermal management needs of aerospace vehicles. The spray cooling work done here was with 95 °C water, and this data is compared to 100 °C water/ propylene glycol spray cooling data from a previous paper so as to compare the spray cooling performance of a single component liquid to that of a binary liquid such as WPG. The module used during this work was a COTS module manufactured by Semikron, Inc., with a maximum DC power input of 180 kW (450 VDC and 400 A).

Effective thermal management and removal of the waste heat generated at diode arrays is critical to the development of high-power solid-state lasers. Thermal design must be considered in the packaging of these arrays. Two different packages with heat dissipation through spray cooling are evaluated experimentally and numerically. Their overall performance is compared with other packaging configurations using different heat removal approaches. A novel packaging design is proposed that can fulfill the requirements of low thermal resistance, temperature uniformity among emitters in the diode array, low coolant flow rate, simplicity and low assembly cost. The effect of temperature uniformity on the pumping efficiency for gain media is examined for our novel packaging design. The thermal stress induced by temperature variation within an emitter is also considered.

For aircraft electromechanical actuator (EMA) cooling applications using forced air produced by axial fans, the main objective in fan design is to generate high static pressure head, high volumetric flow rate, and high efficiency over a wide operating range of rotational speed (1x∼3x) and ambient pressure (0.2∼1 atm). In this paper, a fan design based on a fan diameter of 86 mm, fan depth (thickness) of 25.4 mm, and hub diameter of 48 mm is presented. The blade setting angle and the chord lengths at the leading and trailing edges are varied in their suitable ranges to determine the optimal blade profiles. The fan static pressure head, volumetric flow rate, and flow velocity are calculated at various ambient pressures and rotational speeds. The optimal blade design in terms of maximum total-to-total pressure ratio and efficiency at the design point is obtained via CFD simulation. A 5-blade configuration yields the best performance in terms of efficiency and total pressure ratio.

The aircraft electromechanical actuator (EMA) cooling fan is a critical component because an EMA failure caused by overheating could lead to a catastrophic failure in aircraft. Fault tree analysis (FTA) is used to access the failure probability of EMA fans with the goal of improving their mean time to failure (MTTF) from ∼O(5×104) to ∼ O(2.5×109) hours without incurring heavy weight penalty and high cost. The dual-winding and dual-bearing approaches are analyzed and a contra rotating dual-fan design is proposed. Fan motors are assumed to be brushless direct current (BLDC) motors. To have a full understanding of fan reliability, all possible failure mechanisms and failure modes are taken into account. After summarizing the possible failure causes and failure modes of BLDC fans by focusing on each failure mechanism, the life expectancy of fan ball bearings based on a major failure mechanism of lubricant deterioration is calculated and compared to that provided in the literature.

Peak pressure, crank angle and induction pressure were measured in cylinder number one of a Ford 4.6 liter Modular engine. Chaos analysis was conducted on these measurements and the phase, waveform, Poincare, and FFT plots are presented. These plots show conclusively that the pressure fluctuation inside a cylinder is a broadband chaos.

In this paper, we address the thermal management issues which limit the lifespan, specific power and overall efficiency of an air-cooled rotary Wankel engine used in Unmanned Air Vehicles (UAVs). Our goal is to eliminate the hot spots and reduce the temperature gradients in the engine housing and side plates by aggressive heat spreading using heat pipes. We demonstrate by simulation that, for a specific power requirement, with heat spreading and more effective heat dissipation, thermal stress and distortion can be significantly reduced, even with air cooling. The maximum temperature drop was substantial, from 231°C to 129°C. The temperature difference (measure of temperature uniformity) decreased by 8.8 times (from 159°C to 18°C) for a typical UAV engine. Our heat spreaders would not change the frontal area of the engine and should have a negligible impact on the installed weight of the propulsion assembly.

The scaling laws of fans express basic relationships among the variables of fan static pressure head, volume flow rate, air density, rotational speed, fan diameter, and power. These relationships make it possible to compare the performance of geometrically similar fans in dissimilar conditions. The fan laws were derived from dimensionless analysis of the equations for volumetric flow rate, static pressure head, and power as a function of fan diameter, air density and rotational speed. The purpose of this study is to characterize a fan's performance characteristics at various rotational speeds and ambient pressures. The experimental results are compared to the fan scaling laws.

The blend of dimethyl ether (DME, CH3OCH3) and propane (C3H8) is a potentially renewable fuel mixture that has the potential to replace diesel in compression ignition engines. The combination can potentially reduce particulate and greenhouse gas emissions compared to a conventional diesel engine operating under similar conditions. However, detailed conceptual and simulation studies must be conducted before adopting a new fuel on a compression ignition engine. For these simulations, accurate chemical kinetic models are necessary. However, the validity of chemical kinetic mechanisms in the literature is unknown for mixing controlled compression ignition (MCCI) engine operating conditions. Hence, in this work, we studied the ignition of dimethyl ether (DME) and propane blends in a shock tube at MCCI engine conditions. Ignition delay time (IDT) data was collected behind the reflected shock for DME-propane mixtures for heavy-duty compression ignition (CI) engine parameters.