Globally, the use of methanol as an alternative fuel has attracted interest because of its low production cost, renewable capacity, and good combustion-related properties (higher thermal efficiency, higher engine power, and lower regulated emissions). In China in particular, there are abundant coal resources, and the technology of using coal to obtain methanol has been perfected with low cost; methanol fuel from coal has become one of the most popular alternative fuels for vehicles.
However, the in-cylinder combustion of methanol also produces a considerable amount of extra toxic emissions, such as alcohols and aldehydes. A team at Zhejiang University has now investigated the impact of methanol–gasoline blends on the pollutant emissions of port-fuel injected spark ignition (SI) engines. A paper on their work is published in the ACS journal Energy & Fuels.
Since the 1980s when China started to develop methanol-utilizing vehicles, methanol−gasoline blends as alternative fuels for vehicles have now been promoted in over five provinces, including Shanxi, Shaanxi, Gansu, Guizhou, and Shanghai.
… the in-cylinder combustion of methanol can also produce a considerable amount of extra toxic emissions, such as alcohols and aldehydes. Wei found that burning methanol−gasoline blends could lead to the rise of unburned methanol and formaldehyde emissions. Zhang investigated unregulated emissions from a low-content methanol−gasoline SI engine and found that the engine-out methanol and formaldehyde increased almost linearly with the methanol content in the mixed fuel. Unburned methanol is toxic and corrosive. It can poison the human nervous and blood systems. Formaldehyde has already been widely recognized as a strong carcinogenic and teratogenic substance, which has significant adverse effects on human health. With the wide promotion of methanol as an alternative fuel for vehicles and the growing emphasis on environment protections, methanol-induced unregulated emissions and their control in SI engines will become critical issues.—Yao et al.
The researchers used a GEELY MR479Q 4-cylinder 4-stroke port fuel injection (PFI) SI engine was selected as the test engine for burning different methanol−gasoline blends at wide-open throttle operating conditions.
For the methanol−gasoline blends used in the engine tests, commercial 93# gasoline was used as the base fuel, and industrial-grade methanol with a purity of 99.9% was mixed in with fractions of 0, 10, 20, 30, 50, and 70% by volume (M0, M10, M20, M30, M50, and M70, respectively). No additives were used in the fuel blends.
An AVL Fourier-transform infrared (FTIR) multicomponent gas analyzer measured all of the engine-out emissions for methanol−gasoline blends at each engine operating condition. Besides the regulated NOx, CO, and non-methane hydrocarbon (NMHC) emissions, the species measured during the engine tests also covered various unregulated emissions, such as alcohols, aldehydes, olefins, alkyne, and aromatic hydrocarbons—the latter two being considered as the important soot precursors.
Among their findings:
NOx, CO, and NMHC emissions were all reduced dramatically when the test engine was fueled with methanol−gasoline blends, and the reduction effect of regulated emissions became more apparent with increasing methanol content in the fuel blends. When fueled with M70, the reductions of NOx, CO, and NMHC emissions of the test engine could be as much as 54.5, 70.9, and 79.9%, respectively, compared with those of pure gasoline.
Other engine-out hydrocarbon emissions such as C2H4, C3H6, and soot precursors like C2H2 and AHCs were also reduced with increasing methanol in the fuel blends.
The methanol in the fuel blends also caused significant increases in engine-out CH3OH and CH2O emissions. When the engine was fueled with M70, the engine-out CH3OH emission reached as high as 500 ppm, and the CH2O emission was almost 4 times as much as that with M0.
For the rest of the emissions, such as C2H5OH, C2H4O, and 1,3-butadiene (C4H6), only a slight influence of methanol was observed during the engine tests.
Dongwei Yao, Xinchen Ling, and Feng Wu (2016) “Experimental Investigation on the Emissions of a Port Fuel Injection Spark Ignition Engine Fueled with Methanol–Gasoline Blends” Energy & Fuels doi: 10.1021/acs.energyfuels.6b01586