Daniel Joseph Styles

Exhaust Gas Recirculation Cooler Fouling in Diesel Applications: Fundamental Studies of Deposit Properties and Microstructure

This article reports on the results of experimental efforts aimed at improving the understanding of the mechanisms and conditions at play in the fouling of exhaust gas recirculation coolers. An experimental apparatus was constructed to utilize simplified surrogate heat exchanger tubes in lieu of full-size heat exchangers. The use of these surrogate tubes allowed removal of the tubes after exposure to engine exhaust for study of the deposit layer and its properties. The exhaust used for fouling the surrogate tubes was produced using a modern medium-duty diesel engine fueled with both ultra-low-sulfur diesel and biodiesel blends. At long exposure times, no significant difference in the fouling rate was observed between fuel types and hydrocarbons levels. Surface coatings for the tubes were also evaluated to determine their impact on deposit growth. No surface treatment or coating produced a reduction in the fouling rate or any evidence of deposit removal. In addition, microstructural analysis of the fouling layers was performed using optical and electron microscopy in order to better understand the deposition mechanism. The experimental results are consistent with thermophoretic deposition for deposit formation, and van der Waals attraction between the deposit surface and exhaust-borne particulate.

Visual Study of In-Situ EGR Cooler Fouling Layer Evolution

Exhaust gas recirculation (EGR) is a major technology to reduce NOx from diesel engines for future emission standards. The implementation of EGR coolers has been a common methodology to provide engine in-cylinder NOx reduction. However, EGR cooler fouling is a common problem. The particulate matter in exhaust tends to form a deposit layer on the wall of the heat exchangers. This effect leads to a reduction of thermal effectiveness of the heat exchangers resulting in insufficient EGR cooling and subsequently higher engine NOx emission.This paper utilized a unique test rig offering visible and infrared optical access to the deposit layer in a simulated diesel EGR cooler to study the evolution of the layer from fresh to heavy deposit. A 460μm thick deposit layer was built during a 37 hour exposure. Time lapse videos were taken provide visual in-situ evidence for the investigation of the layer thickness development and morphology change during the deposition. The layer growth tended to stabilize from about 22 hours of deposition. The shear force exerted by the gas flow moves surface particles of 20μm in diameter or larger. This could contribute to the stabilization phenomenon.Copyright

3-D Numerical Study of Turbulent Mixing of Intake Air and Exhaust Gas in a Low Pressure EGR System

A 3-D numerical study of turbulent mixing characteristics of air and exhaust gas in a low pressure EGR system (LP-EGR) has been performed under typical operating conditions. There are two objectives of this study. The first objective of the study is to understand and quantify the effects of following factors on mixing quality of exhaust gas and intake air: a) Rate of generation and dissipation of turbulence in the near mixing zone. b) Swirl induced due to formation of counter rotating vortex pairs (CVPs). c) Impingement of the EGR jet on the opposite wall of the intake manifold. The second objective of this study is to understand mixing quality with respect to pressure drop. Under typical conditions, on the low pressure side of the turbocharger, the pressure drop available to ensure required mass flow rate of EGR into the intake air is minimal. Hence, different EGR inlet configurations have been modeled to calculate the mixing quality along with the pressure drops. Some of configurations that have been studied are the effect of varying the diameter of EGR inlet tube, varying the insertion of EGR inlet tube into the intake air duct, angular injection, mixing elbow, multi-point EGR injection, EGR tube with multiple nozzles, venturi configuration, EGR flow control valve at EGR inlet etc. The above mixers have been compared by plotting respective mixing quality vs. EGR-side pressure drop and air-side pressure drop on a 3-D scatter plot at various operating conditions of the engine. One of the important conclusions of the study is that, in the range of operating conditions considered, a simple T-Junction like configuration, which generates maximum local turbulence and allows uninhibited formation and propagation of counter rotating vortex pairs, provides the best mixing quality with the least pressure drop.Copyright