The Society for Automotive Engineers (SAE) has published a new set of standards for calculating emissions and fuel economy (J1711), updating the original standard from 1999.  The new standard addresses the calculations required for alternative vehicles such as electrics and hybrids.

The revised standard is titled Recommended Practice for Measuring the Exhaust Emissions and Fuel Economy of Hybrid Electric Vehicles, including Plug-in Hybrid Vehicles (J1711 JUN2010).  The new procedures aim to more accurately measure the exhaust emissions and fuel economy of hybrid electric vehicles (HEV) and plug-in hybrid electric vehicles (PHEV).  They go a long way towards better understanding and quantifying how hybrids compare to standard internal combustion-only vehicles.  The SAE standards are important because the Environmental Protection Agency (EPA) routinely uses them as the basis for their own ratings, which are required to appear on the window sticker.

With the operational possibilities of hybrids, especially PHEVs, SAE felt it was necessary to update standards to better accommodate these alternative cars.  The structure of these procedures allow for any of the five major test cycle procedures to be substituted as required for the vehicle being tested.  For instance, exhaust pipe emissions testing is pointless on an all electric car while accounting for PHEV electric car driving mode is not needed in a non-plug-in hybrid (HEV).

Which emissions to test for are according to the tester’s needs as SAE does not set standards or limits on emissions – that is the EPA’s purview.  Two basic definitions for vehicle types are given in order to define a hybrid:

1. A vehicle using consumable fuels, which are defined as petroleum-based liquids (e.g. gas, diesel), alcohol-based liquids (e.g. methanol, ethanol), and hydrocarbon-based gases (e.g. natural gas).
2. A recharchable energy storage system (RESS) that is recharged by either an on-board hybrid propulsion system, an external energy source, or both.  Energy storage systems are defined as batteries, capacitors, and electromechanical flywheels.

From there, two economy and emissions tests are given.  The first begins with the vehicle’s operation in a Charge-Sustaining Test (CST) in which a hybrid would be using an internal source (consumable fuel).  The other assumes an external source has powered the energy storage system and is a Full Charge Test (FCT).

All hybrids that meet the J1711 definition will receive the CST test while only those using an RESS (meaning PHEVs) will also use the FCT.  These two tests are the bulk of the changes that SAE made to the alternative vehicles addition for the J1711 standard.

If both tests are used, then another calculation is made to give the vehicle a Utility Factor (UF) weighting for the FCT data.  A vehicle with a relatively long range as an all electric car before the ICE begins charging would have a much higher utility weight than a car with a short range.  These numbers are based on the national average for driving, so a vehicle with an electric car range of 15 miles would have a UF of about 0.5 (roughly half the national average in miles per day) while one with a range of 3 miles all electric would have a UF closer to 0.1.

The UF is used to weight how much of the alternative vehicles’ total economy test is based on the FCT in proportion to the CST.  Thus a Fisker Karma would have a higher total J1711 FCT number than would a Plug-in Toyota Prius due to the Karma’s much longer all electric car range.

Two things not included in the new J1711 standards are tests to give MPG equivalent for an electric car (a battery electric or all electric car) and for EV cars based on hydrogen fuel cells (HFEV).

Since hydrogen fuel cells have no emissions outside of the water from their exhaust and since electric cars are tailpipe emissions-free, neither fall into the standard given by SAE.  This is probably best since a miles per gallon equivalent is really unnecessary for these types of vehicles.  They only confuse the issue for consumers.

After all, while most consumers are vaguely aware that both electricity and hydrogen come from sources that are likely putting out emissions, those sources are variable by location and source and their costs will also vary by location and source.  So attempting a blanket calculation for their “emissions” would be foolhardy.

In the end, these new standards from SAE will probably prompt the EPA to begin considering a change to how MPG is calculated for the U.S. stickers on vehicles at the lot.

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