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The National Research Council (NRC) recently published a report entitled “Effectiveness and Impact of Corporate Average Fuel Economy (CAFE) Standards” intended to help U.S. policymakers in the formulation of CAFE policy. In the Report, the NRC projects fuel consumption reductions from the application of a wide range of engine, transmission, and vehicle technologies. The Report employs a simple multiplicative method to aggregate the effects of multiple technologies on fuel consumption. In this paper, a basic energy balance calculation is used to examine the NRC results against theoretical limits. Theoretical limits are calculated using measured and simulated breakdowns of system energy losses incurred during vehicle operation on EPA driving cycles. This analysis demonstrates the inherently optimistic results produced by simple aggregation methodologies. Methods for enhancing the accuracy of the technology-aggregation process are proposed.

In the twenty-first century, exhaust emission control will remain a major technical challenge especially as additional pressures for fuel and energy conservation mount. To address these needs, a wide variety of engine and powertrain options must be considered. For many reasons, the piston engine will remain the predominant engine choice in the twenty-first century, especially for conventional and/or parallel hybrid drive trains. Emissions constraints favor the conventional port fuel-injected gasoline engine with 3-way exhaust catalyst, while energy conservation favors direct-injection gasoline and diesel engines. As a result of recent technological progress from a competitive European market, diesels, and most recently, direct-injection (DI) diesels now offer driveability and performance characteristics competitive with those of gasoline engines. In addition, DI diesels offer the highest fuel efficiency.

Air velocities at several points near the spark plug location were measured using a laser Doppler anemometer (LDA) in a motoring internal combustion engine. This engine was equipped with three intake configurations: a standard valve in a standard port, a standard valve in a helical (swirl) port, and a shrouded valve in a standard port. Both ensemble-averaged and cycle-resolved mean velocities were determined; this allows comparison of rms velocity fluctuation, cycle-resolved turbulence, and cycle-by-cycle variations in mean velocity. Frequency domain analysis of these components was also carried out. The main conclusion of this experimental study was that starting from a very low swirl situation (standard valve case), addition of a moderate amount of swirl (swirl port case) goes a long way towards improving cycle repeatability and increasing cycle-resolved turbulence. Increasing swirl even further (shrouded valve case) does not produce further dramatic improvements.

This research demonstrates the capability of the Laser Doppler Anemometer (LDA) for making measurements inside a piston-engine cylinder. The backscatter mode of LDA operation, requiring only a single window in the cylinder, was used. An ensemble-average data-processing technique has been developed to analyze the raw velocity-crankangle data. Single-component measurements of mean velocity and rms velocity fluctuation at a single point are presented as functions of crankangle for three engine speeds. A comparison of motored and fired results is shown for one engine speed. Measurements of two components of velocity at several locations show the basic vortical nature of the flow field in this particular engine.