Study suggests Mexico’s PEMEX branded diesel fuels comparable to US diesel

US trucker smoking!
Why are we worrying about a few Mexican trucks when we have thousands of our own polluting the landscape?
At one time or another, we’ve all heard Dale “The Trucking Bozo” Sommers, or his kid Steve and Eric “Bubba Bo” Bolanger from ATN preaching the gospel to anyone of their dwindling number of listeners, that Mexican diesel is garbage fuel, thick, contaminated, green slime, not fit to be burned in a ships bunker. And lamentably, many beliefs these self righteous talkers.

However, a report has come to light by the Texas Transportation Institute, part of the Texas A&M University system that suggests the diesel fuel processed and sold in Mexico, by PEMEX, is equal to and in some cases exceeds EPA standards, post 2007.

I’m not going to go into a lot of detail here. You can download and assess the report HERE, but needless to say, the report debunks many of the claims made by opponents of Mexican trucks who continue to grasp at an ever dwindling bunch of straws to discredit the program.

The overall goal of this scientific study was to quantify emissions produced by Mexican trucks operating on standard diesel and alternative fuels. Vehicle testing was conducted near the Colombia Commercial Bridge, just outside of Laredo, Texas. A sample of five Mexican drayage trucks and five Mexican long-haul trucks were selected for testing. Each truck was subjected to long-haul and drayage drive cycles while operating with three different fuel types and pulling a trailer that had been loaded to a specified weight. Emissions data was collected using portable emissions measurement system (PEMS) equipment.

The study measures the emissions for Mexican trucks using three types of fuel – the standard diesel available in Mexico, sold by PEMEX. ULSD fuel (mandated by the U.S. Environmental Protection Agency [EPA] for use in 2007 and later model trucks in the U.S.), and a biodiesel mix (20 percent biodiesel fuel and 80 percent ULSD fuel). A detailed description of these fuels can be seen in the source document.

The procedure involved testing emissions of carbon monoxide (CO), carbon dioxide (CO2), oxides of nitrogen (NO and NO2 – collectively referred to as NOx), total hydrocarbons (THC), and particulate matter (PM). Sampling was also performed for mobile-source air toxics (MSATS) under idling conditions. The existing vehicle fleet participating in cross-border trucking was first profiled and a representative sample of trucks was selected. Testing was conducted for the three different fuel types on the selected trucks following pre-determined drive cycles. The research team used two PEMS units for the testing.
[pullquote]In general, the results of this study suggest that using the ULSD fuel instead of the PEMEX fuel might not provide the expected emissions benefit.[/pullquote]
RESULTS & CONCLUSIONS

NOx Emissions

It was found that for idling modes (low and high) the B20 and PEMEX fuels tend to decrease NOx emissions slightly (compared to the ULSD fuel). For on-road modes (drayage and long-haul cycles), both the B20 and PEMEX fuels seemed to increase NOx. There was no clear correlation between vehicle age and NOx emissions rates. The impact of air conditioner usage on NOx was mixed; with a notable impact in idle mode and no apparent effect for on-road tests.

HC Emissions

Both the B20 and PEMEX fuels reduced hydrocarbons emissions during all modes of operation when compared to the ULSD fuel with the B20 fuel having the highest reduction. The age of the trucks appeared to have an inverse effect (newer trucks showed higher emissions) on HC emissions, which might be the result of finer fuel injection in newer diesel engines. The effect of air conditioning usage on HC was not clear because of the mentioned inverse impact of age on HC.

CO Emissions

Similar to HC emissions, the B20 and PEMEX fuels tended to decrease CO emissions compared to the ULSD fuel for all operation modes. It was found having a newer engine does not appear to have a positive impact on CO emissions rates in the idling mode as would be expected. The results were mixed for on-road tests: no age impact was observed for long-haul trucks. Newer drayage trucks had lower CO emissions than the older ones. There was no obvious correlation between air conditioning usage and changes in CO rates.

CO2 Emissions

The results showed that the fuel type does not have an impact on the CO2 emissions. However, it must be noted that 20 percent of the B20 fuel came from a renewable source. CO2 from this portion can be considered as an emission benefit. Air conditioning appeared to have a notable impact on CO2 emissions. The age of the trucks showed no apparent effect on CO2 emissions.

PM Emissions

The B20 fuel appeared to substantially reduce PM emissions (from the ULSD fuel) for the on-road operational mode. The PEMEX fuel also seemed to reduce PM, but to a lesser extent. The PEMEX fuel used had a higher cetane index as compared with the ULSD fuel (50.2 versus 47.5). Previous studies have shown that higher cetane numbers can increase NOx slightly and reduce CO and HC. All else equal, higher cetane tends to advance the ignition timing which causes a decrease these emissions and a slight increase in NOx. The increase in NOx would be most obvious on the driving cycles where the engine is under load. Additionally, the process to lower the sulfur to develop the ULSD fuel could involve the addition of hydrogen that might result in higher PM numbers. There is also a potential lubricity effect (contaminants in the fuel system mixes into the fuel line) resulting in higher than expected emissions rates, especially for PM.

Mobile Source Air Toxics

The formaldehyde and acetaldehyde emissions were significantly lower than observed previously in idling trucks from the U.S. and Mexico. The higher cetane index of all three fuels may be responsible for this observed reduction. No additional aldehyde emissions were detected from the biodiesel fuel, despite its fuel oxygen. Because the new ultralow sulfur rules have improved fuel quality in both the U.S. and Mexico, there is no reason to expect that ULSD or B20 fuels would have a noticeable effect on the aldehyde MSAT emissions.

In general, the results of this study suggest that using the ULSD fuel instead of the PEMEX fuel might not provide the expected emissions benefit. But as this carefully conducted scientific study shows, and contrary to what you’ve been led to believe, in most cases, PEMEX diesel fuel is comparable to USLD and can produce lower emissions, clearly debunking the claims of OOIDA and other opponents of cross border trucking who use environmental issues to cloud the debate over Mexican trucking.
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