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November 01, 2006  |   Comments (0)   |   Post a comment

Too Good to Be True? (Part 2)

An engineering expert takes exception to the promises of better fuel economy, extended oil intervals and reduced emissions made by suppliers of fuel additives, engine attachments and other aftermarket products. The second of a two-part article.

by Dan Herman


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In the discussion that appeared in the June/July 2006 issue (“Too Good to Be True?” beginning on pg. 70), I introduced you to the common claims aftermarket suppliers of attachments and additives make for their products. It concluded with a discussion of how, if these products really worked, the U.S. Environmental Protection Agency (EPA) and the engine manufacturers would quickly adopt them for competitive and economic reasons.

If you don’t agree with that argument and believe that supplementary devices or additives will contribute to a better running engine, this installment will give you some questions to ask your provider to ensure that the product claims are valid. The basic question is: “Where’s your data?” Expansions of that question follow.

Reduced emissions
In the EPA emissions regulations, the content of the four major ingredients defined in the first part of this article (particulate matter, hydrocarbons, oxides of nitrogen and carbon monoxide) is measured on a mass basis in grams per brake horsepower-hour (g/BHP-hr).

Aftermarket suppliers will make claims to reduce some or all of these factors, sometimes with accompanying numbers and sometimes not. If the claims include numbers, they may be just percentage reductions and/or quantitative values. The numbers are usually expressed in parts per million (PPM) for HC, NOx and CO and percent opacity (a measure of light transmission through the exhaust stream) for particulate matter (PM).

Note that these are different scales than the EPA requirements. There is no correlation or conversion between PPM and g/BHP-hr nor any correlation between opacity and g/BHP of particulate matter. In fact, the smoke output of diesel engines manufactured after 1994 is so low that it would be difficult to measure an opacity level on a properly maintained engine. These values are obtained by “field” test equipment that is portable and inexpensive and test procedures that involve “sniffing” the tailpipe while the vehicle is at rest with the engine unloaded or on a chassis dynamometer with the engine operating conditions uncontrolled. There is just no way to relate these tests to the certification procedure that the engine manufacturer must follow.

The only legitimate test method for heavy-duty engine emissions performance is the EPA-designed transient emissions test cycle on an engine dynamometer. This procedure involves operating the engine from cold start through a cycle including no-load idle, acceleration, cruise, deceleration, etc., to simulate on-road operation of a vehicle.

The four major emissions components are measured with highly sensitive, expensive equipment; a test cell can cost several million dollars. This is the only method of certifying an engine or a modification to an engine that the manufacturers can use with the EPA. Ask the aftermarket supplier to provide certified test results per the EPA transient test cycle from an EPA-approved laboratory, such as Southwest Research Institute in San Antonio, Texas (www.swri.edu), that show the magnitude of emissions performance improvement that they attribute to the use of their attachment or additive, in the same engine sample, with and without the modification. Any other test method or data is inconsistent and irrelevant.

Increased fuel economy
Claims for this factor are usually supported by customer testimonials about fleet operating experience. Fleet operation evaluation of fuel economy is highly inaccurate. The fuel consumption of the vehicles is affected by many factors other than the material being tested: driver behavior, season of the year, weather conditions, variations in traffic conditions, variation in vehicle loads, etc. These factors can easily be more influential than the impact of the test material.

I cite a personal experience as an illustration: Once, when we were seeking locations for field-testing a new engine product, we found a truck operator who had very good fueling records and carefully maintained vehicles. We chose a candidate test vehicle that was operated by the same driver, over the same general route, with some variation in load. They were able to provide a tabulated one-year summary of fuel consumption on the candidate vehicle with average fuel economy calculated each month. Across that one-year period, the monthly fuel economy varied by 14 percent from minimum to maximum. That variation was much greater than the improvement we hoped to achieve with the new engine. There are too many uncontrolled variables in fleet operation that affect fuel consumption and distort the analysis of the test product.

The only true measure of comparative fuel economy in a complete vehicle is the Society of Automotive Engineers (SAE) “Type II Test.” In this procedure, to evaluate the impact of a fuel additive, you would choose two similar but not necessarily identical vehicles.

For instance, two 65-passenger Type C school buses would be a good match. The make and engines don’t have to be the same. One vehicle is operated throughout the test regime unchanged — same vehicle, same attachments, same fuel in each test. This is the baseline vehicle. The second vehicle is modified with the test material, either an attachment or an additive. Only one modification can be tested at a time. The vehicles are operated over a closed course with the drivers practicing the drive until the course can be completed in the same time interval within 2 percent repeatability.

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