James C. Conklin

A proposed methodology for estimating transient engine-out temperature and emissions from steady-state maps

Abstract Many vehicle systems simulations utilize engine maps constructed from steady-state dynamometer measurements to estimate exhaust temperature and emissions as functions of engine speed and load. Unfortunately, steady-state engine behaviour is often significantly different from actual behaviour under transient driving conditions. This is particularly true for vehicles that undergo repeated engine shutdown and restart (e.g. electric hybrids). The authors propose a methodology for estimating transient engine exhaust properties and fuel economy based on corrections to steady-state maps. The suggested methodology has been implemented in the Powertrain Systems Analysis Toolkit (PSAT) and this implementation is used to demonstrate good agreement with experimental measurements for both a light-duty diesel and a flex-fuel gasoline/ethanol engine. Specific procedures are also recommended for setting key parameters required by the proposed methodology and possible directions for further improvements are suggested.

Multi-dimensional simulations of cold-start transients in a catalytic converter under steady inflow conditions

A multi-channel model is used to study the impact of flow non-uniformity during cold-start transient operations of a catalytic converter. It is seen that inlet zone recirculation can lead to significant non-uniformity of the flow in the monolith, and this non-uniformity can lead to significant differences in ignition characteristics among the channels. These ignition differences are especially pronounced at lower exhaust temperatures, where the axial location of ignition can vary from one channel to another. It is suggested that this strong effect of temperature on ignition may explain some of the apparently contradictory conclusions about the impact of flow non-uniformities in the literature. The simulations here show that the index of non-uniformity, as defined in many past studies, is an inadequate measure of the full impact on ignition characteristics. For the same index of non-uniformity, the non-uniformity effects on ignition become less significant with increasing exhaust flow rate. This implies that more detailed simulations of flow and temperatures non-uniformities caused by the recirculation zones, heat losses at the boundaries and insufficient mixing upstream of the monolith can be relevant to practical applications.

A Unique Approach to Power Electronics and Motor Cooling in a Hybrid Electric Vehicle Environment

An innovative system for cooling the power electronics of hybrid electric vehicles is presented. This system uses a typical automotive refrigerant R-134a (1,1,1,2 tetrafluoroethane) as the cooling fluid in a system that can be used as either part of the existing vehicle passenger air conditioning system or separately and independently of the existing air conditioner. Because of the design characteristics, the cooling coefficient of performance is on the order of 40. Because liquid refrigerant is used to cool the electronics directly, high heat fluxes can result while maintaining an electronics junction temperature at an acceptable value. In addition, an inverter housing that occupies only half the volume of a conventional inverter has been designed to take advantage of this cooling system. Planned improvements should result in further volume reductions while maintaining a high power level.

Intra-Channel Mass and Heat-Transfer Modeling in Diesel Oxidation Catalysts

We consider the effect of intra-channel mass and heat transfer in modeling the performance of diesel oxidation catalysts. Many modeling studies have assumed that the intra-channel flow is laminar and, thus, heat and mass transfer between the bulk gas and wall are appropriately described using correlations for fully-developed laminar flow. However, recent experimental measurements of CO and hydrocarbon oxidation in diesel exhaust reveal that actual mass-transfer rates can deviate significantly from those predicted by such correlations. In particular, it is apparent that there is a significant dependence of the limiting mass-transfer rate on the channel Reynolds number. Other studies in the literature have revealed similar behavior for heat transfer. We speculate that this Reynolds number dependence results from boundary-layer disturbances associated with washcoat surface roughness and/or porosity. When we apply experimental mass and heattransfer correlations to multichannel simulations of a diesel oxidation catalyst, the steady-state conversions differ significantly from those obtained assuming fully-developed laminar flow. These results suggest that assuming fully-developed laminar flow may not always be appropriate.

Performance Evaluation of a Prototype TurbX™ Engine

A revolutionary new concept internal-combustion engine called TurbX™ was invented and a prototype was built by an independent inventor, M. A. Wilson. Theoretically, the TurbX™ engine cycle can be represented by the Atkinson thermodynamic cycle with a continuous combustion process. Because of these attributes, this concept has the potential for higher fuel economy and power density relative to other internal combustion engine types. To evaluate the performance of this prototype, Oak Ridge National Laboratory and The University of Tennessee conducted an independent experimental study. Two series of tests were performed: cold-flow and fuel-fired tests. Cold-flow, compressed-air driven, tests were performed by pressurizing the combustion chamber with shop air to demonstrate the prototype performance of the turbine section. These results showed positive but unremarkable torque for combustion chamber air pressures above 300 kPa with a functional relationship illustrative of typical gas turbines with respect to shaft speed. The fuel-fired tests consisted of 26 constant-speed runs between 1800 and 9500 RPM. The experimental apparatus limited the maximum test speed to 9500 RPM. The TurbX™ engine produced no net output power for all fuel-fired tests conducted. The temperature measurements indicated that for most of the runs there was sustained combustion. However, even in runs where satisfactory combustion was observed, measured gage pressure inside the combustion chamber never exceeded 15.5 kPa. The lack of sufficient pressure rise inside the combustion chamber is indicative of excessive leakage of the combustion products through the preliminary prototype engine internals. Based on the results and the experience gained through this independent testing of this preliminary prototype, further development of this concept is recommended. Three major issues are specifically identified: 1) the internal components must be redesigned to reduce leakage, 2) combustion chamber design and 3) improve the overall aerodynamic performance of the engine internal components.Copyright