Despite problems with its characteristics (toxicity; handling, storage and delivery requirements; and materials compatibility), methanol attracted a great deal of interest in the 1970s and later as an alternative fuel, partly because it can be produced from a number of raw and renewable resources. Indeed, methanol was a past US alternative fuel of favor; in 1989, President George H. W. Bush called for one million cars in the most polluted areas in the US to be running on methanol, ethanol or natural gas by 1997.

Work on liquid methanol-fueled combustion engines was largely dropped in Europe and the US by the end of the 20^th century, the Tsinghua authors noted, largely because of the high cost of production of methanol, which was generated primarily from natural gas.

However, the use of coal-generated methanol as a practical alternative fuel is one of the most realistic options for China, because of the “oil-lean, gas-lacking, and coal-rich” structure of Chinese energy resources.

—Fan et al.

While the influences of methanol content on the combustion characteristics, fuel economy, and regulated emissions of gasoline engines has been widely researched, the unregulated emissions resulting from methanol blend combustion have been less studied, the researchers said.

Unburned methanol and formaldehyde emissions from methanol engines are harmful to the environment as well as to human health. If low-content methanol-gasoline blended fuels are used in current port fuel injection (PFI) gasoline engines, the conversion efficiencies of unburned methanol and formaldehyde emissions on the conventional three-way catalyst (TWC) need to be intensively evaluated. Previous experimental studies have mainly concentrated on the measurement of engine-out unregulated emissions from methanol-gasoline engines rather than tailpipe-out emissions.

...there is a need for a reliable measurement method with high accuracy and good repeatability, to evaluate the use of low-content methanol-gasoline blended fuels directly in current PFI gasoline engines. The derived method should have the ability to comprehensively assess the characteristics of engine-out and tailpipe-out unregulated emissions.

—Fan et al.

The researchers devised an engine test bench, and evaluated gasoline, M10, M15, M20, and M30 methanol-gasoline blends in a four cylinder port fuel injection (PFI) gasoline engine (EQ491i) without any modification. A Fourier transform infrared (FTIR) spectrometer was used to measure the unregulated emissions before and after a conventional three-way catalyst.

Among the findings and conclusions of the study were:

• When an engine works around the gasoline stoichiometric ratio (14.5), the increment of methanol in blended fuels has only a slight influence on engine thermal efficiency and energy economy.

• The cylinder pressure and heat release rate do not obviously vary with the increment in the methanol content in the fuels. The COV (coefficient of cyclic variation) difference gradually decreases as the methanol content increases, especially at low load. The MBF50% (mean burn fraction) position advances as the methanol content increases, especially at high load.

• Engine-out methanol and formaldehyde, as unregulated emissions, increased almost linearly with the methanol content in the fuel, while the ethanol and acetaldehyde emissions were little influenced by methanol addition.

• For low-content methanol-gasoline blended fuels, CO, NO_x, and THC emissions (i.e., regulated emissions) before the catalyst do not vary remarkably with increments in the methanol content of blended fuels. Levels of regulated emissions from blended fuels after the catalyst are the same as those for pure gasoline.

• The methanol content in low-content methanol-gasoline blended fuels has a large influence on methanol and formaldehyde emissions but only a slight influence on ethanol and acetaldehyde emissions. Methanol, ethanol, formaldehyde, and acetaldehyde emissions after the catalyst were the same as those for pure gasoline.

Because tailpipe-out methanol and acetaldehyde emissions were similar to those for pure gasoline under warmed-up, steady-state conditions, the use of low-level methanol blends would not be expected to increase these emissions in widespread use. Conventional TWCs used in present gasoline engines could solve the problem of unregulated emissions from methanol blends. To investigate the transient exhaust emissions, cold-start and driving cycle tests should be carried out in further work.

—Fan et al.

The research was supported by the National High Technology Research and Development Program of China (“863” Program) “Adaptability Research on Methanol Vehicle”, under Grant 2006AA11A1A4.

Resources

• Zhang Fan, Zhang Xia, Shuai Shijin, Xiao Jianhua and Wang Jianxin (2009) Unregulated Emissions and Combustion Characteristics of Low-Content Methanol-Gasoline Blended Fuels. Energy Fuels, Article ASAP doi: 10.1021/ef900974p