Richard B. Bramlette

Employing Adaptive Mesh Refinement for Simulating the Exhaust Gas Recirculation Mixing Process

One significant emissions issue of compression ignition engines that directly influences human health is the production of nitrogen oxides (NOx). Once produced, these species are difficult to convert catalytically in the exhaust and often require a complex aftertreatment system to mitigate their release into the environment. The common methodology by the internal combustion engine community to reduce the amount of NOx is to employ Exhaust Gas Recirculation (EGR) in order to dilute the intake mixture with inert species (e.g., water). This lowers the combustion temperature lessening the thermal NO production mechanism. Improper mixing of EGR with the intake (species in-homogeneity, low levels of mixing turbulence, etc.) can lead to significant cylinder-to-cylinder variation in combustion temperatures and NOx emissions, making it more difficult to achieve regulatory standards.In this effort, a three-dimensional (3-D), transient, computational fluid dynamics (CFD) analysis was performed in order to more accurately model the mixing of EGR and intake for a single-cylinder test engine. Mixing is achieved for this engine by using a small rectangular box in which clean air and engine exhaust for controlled recirculation are mixed prior to engine intake. A matrix of computational analyses at different engine loads, and simulation types (large eddy and Reynolds-averaged Navier-Stokes) at 25% EGR were performed to check computational time and agreement with experimental measurements. Moreover, this effort employs the use of adaptive mesh techniques in order to understand their usage and validate correct implementation for later endeavors including more complex geometries, such as the manifold of a multi-cylinder engine. The simulation results indicate that mass flow rate and temperature of the mixture as it leaves the mixing box agree to within 3% of experimental values. Furthermore, pressures at the air and EGR inlet boundaries showed agreement to around 1% and 12%, respectively, with the experimental measuring points indicated as the reason for the difference. In addition, species mixing of carbon monoxide was uniform to within 440 ppm. Finally, the use of the models may also account for a prior discrepancy in the output power of the single-cylinder engine test stand.Copyright

Steerable Adaptive Bullet (StAB) piezoelectric flight control system

This paper outlines a new class of piezoelectric flight control actuators which are specifically intended for use in guided hard-launched munitions from under 5.56mm to 40mm in caliber. In March of 2011, US Pat. 7,898,153 was issued, describing this new class of actuators, how they are mounted, laminated, energized and used to control the flight of a wide variety of munitions. This paper is the technical conference paper companion to the Patent. A Low Net Passive Stiffness (LNPS) Post Buckled Precompressed (PBP) piezoelectric actuator element for a 0.40 caliber body, 0.50 caliber round was built and tested. Aerodynamic modeling of the flight control actuator showed that canard deflections of just ±1° are more than sufficient to provide full flight control against 99% atmospherics to 2km of range while maintaining just 10cm of dispersion with lethal energy pressure levels upon terminal contact. Supersonic wind tunnel testing was conducted as well as a sweep of axial compression. The LNPS/PBP configuration exhibited an amplification factor of 3.8 while maintaining equivalent corner frequencies in excess of 100 Hz and deflection levels of ±1°. The paper concludes with a fabrication and assembly cost analysis on a mass production scale.

Semi-solid state adaptive impedance composites for HIRF protection

The feasibility of piezoelectric-based Adaptive-Impedance Composites (AIC) as a method of protecting aircraft equipment from lightning strike events and the resultant High-Intensity Radiated Fields (HIRF) was investigated. Classical Laminated Plate Theory (CLPT) and sheet vibration theory were applied to analytically derive the performance of the AIC. Multiple prototypes were built for high voltage testing which revealed closed- to open-circuit switching as fast as 77 μs. It was observed that slight geometric variations of the AIC strongly influenced the activation voltage. The voltage necessary to trigger the 85mm long, 3rd generation AICs impedance could be set between 10 and 60 V. The test data and the analytical predictions were compared with the lightning strike data gathered by ONERA. The comparison indicated the AIC switching speed was over 30 times faster than the necessary minimum to shield typical avionics and flight control mechanisms from lightning-strike induced electrical eddy currents and HIRF.