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As part of the EPA's ongoing in-use vehicle emissions compliance program, two hybrid vehicles were tested. A 2001 Honda Insight and a 2001 Toyota Prius were tested on a chassis dynamometer at the National Vehicle Fuel and Emissions Laboratory. Both vehicles were run on the Federal Test Procedure drive cycle. Emissions were measured simultaneously using the SEMTECH-G Portable Emissions Measurement System (PEMS) for comparison to the chassis dynamometer bench analyzer. The correlation for cumulative emissions (bag) between dynamometer and on-board analyzer were adequate for CO2, CO, and NOx, though the PEMS HC measurements were low by comparison. The measurements were limited by the very low exhaust volume flow rates on both vehicles. A more sensitive flow meter will be required to measure emissions from vehicles certified to SULEV standards.

The potential discrepancy between the fuel economy shown on new vehicle labels and that achieved by consumers has been receiving increased attention of late. EPA has not modified its labeling procedures since 1985. It is likely possible that driving patterns in the U.S. have changed since that time. One possible modification to the labeling procedures is to incorporate the fuel economy measured over the emission certification tests not currently used in deriving the fuel economy label (i.e., the US06 high speed and aggressive driving test, the SC03 air conditioning test and the cold temperature test). This paper focuses on the US06 cycle and the possible incorporation of aggressive driving into the fuel economy label. As part of its development of the successor to the MOBILE emissions model, the Motor Vehicle Emission Modeling System (MOVES), EPA has developed a physically-based model of emissions and fuel consumption which accounts for different driving patterns.

The new EPA emissions inventory model, MOVES (MOtor Vehicle Emissions Simulator) models fuel consumption of the on-road fleet in its first draft (2004 version). Future versions will model criteria pollutants. MOVES is designed to combine fleet, activity, and second by second emission rate inputs to produce regional, or national fuel consumption rates. It is primarily a data driven model but for some of the future projections, data is not available. It is necessary to design a model, which can fill these “holes” and future emissions rates in MOVES. The Physical Emissions Rate Estimator (PERE) takes vehicle and drive cycle inputs and simply distributes the energy required to follow the trace to the various components (internal combustion engine, electrical motor, fuel cell, etc). The model is validated to the certification fuel economy of the Honda Insight, Honda Civic, Honda FCX, Toyota Prius (2001, and 2004). It is also compared to a small subset of second by second data.

In a continuing effort to include real-world emissions in regulatory testing, the USEPA has included air conditioning operation as part of the Supplemental Federal Test Procedure (SFTP). Known as the SC03, these tests require automobile manufacturers to construct and maintain expensive environmental chambers. However, the regulations make allowances for a simulation test, if one can be shown to demonstrate correlation with the SFTP results. We present the results from an experiment on a 1998 Ford sedan, which simulates the heat load of a full environmental chamber. Moreover, the test procedure is simpler and more cost effective. The process essentially involves heating the condenser of the air conditioning system by using the heat of the engine, rather than heating the entire vehicle. The results indicate that if the head pressure is used as a feedback signal to the radiator fan, the load generated by a full environmental chamber can be duplicated.

A number of spark ignition engines from 1997 to 2003 are analyzed for their overall friction characteristics using the Willans line approach. This methodology appears to be quite robust across many different types of engines. Using a variety of partial and complete engine maps from multiple manufacturers, it is confirmed that engine friction has been decreasing over the decades (compared to past studies). Overall there has been a 25% reduction over 30 years. It is also demonstrated that thermal efficiency (defined here as the slope of fuel mep and bmep excluding enrichment) has been remaining steady during the same period. The application to aggregate engine models is discussed.

The emission of excessive quantities of NOx when the automobile air conditioner is turned on has received a fair amount of attention in recent years. Since NOx is a smog precursor, it is important to understand the reasons for this jump in emissions especially on hot sunny days when air conditioner usage is at a maximum. A simple thermodynamic model is used to demonstrate how the torque from a typical air conditioner compressor is mainly related to the ambient temperature. The compressor's on-off cycling patterns are also characterized. Since the compressor significantly loads the engine, it affects fuel economy and emissions. The key independent variable that we employ to represent engine load is fuel rate. The correlations between engine-out NOx emissions and fuel rate are shown for a number of light duty vehicles and trucks. From these, a physical model for engine-out NOx emissions (with and without air conditioning) is presented.