Mexican Gasoline Additives May Reduce Engine Efficiency

Variations in gasoline additive compositions across brands in Mexico may accelerate engine efficiency deterioration compared to other countries, according to the Gasoline Quality Evaluation Project (Phase Three). The study, conducted by the Faculty of Chemistry at the National Autonomous University of Mexico (UNAM) and the Mexican Association of Automotive Dealers (AMDA), underscores inconsistencies in fuel quality nationwide.

Presented at the "Combustibles en México" forum, the study highlights irregular levels of MTBE (methyl tert-butyl ether) and TAME (tert-amyl methyl ether), compounds used to enhance octane ratings. “Engines designed for a specific octane level will perform differently if that value changes,” explained Humberto Gómez Ruiz, an environmental analytical chemistry expert. “Proper octane ratings are essential for optimal engine performance.”

The study detected heavy hydrocarbons—molecules with more than 16 carbon atoms—in multiple fuel samples. These substances do not evaporate efficiently under standard conditions, causing ignition instead of controlled combustion. Such inefficiencies can lead to gum deposits that clog fuel injectors and valves, thereby diminishing engine performance.

The report also revealed significant disparities in ethanol concentrations among fuel brands. US gasoline contained 9.90% ethanol, while brands like G500, BP, Arco, and Valero showed concentrations below 1%. While ethanol can boost octane ratings and reduce emissions, it may adversely affect engines not designed for high-ethanol blends.

MTBE levels also varied widely: Repsol (9.48%) and Shell (9.24%) recorded the highest concentrations, while Chevron had the lowest at 3.82%. These inconsistencies can impact combustion efficiency and engine output.

“The entire fuel supply chain, from importers to service stations, must ensure compliance with quality standards,” stated Rodolfo Lacy Tamayo, a PhD in Environmental Science and Engineering. “Despite nearly 200 certified labs in Mexico, quality verification remains insufficient, as evidenced by past fuel supply challenges.”