Although biodiesel can be directly applied without making large adjustments to the engine, since biodiesel is a mixture of saturated fatty acid methyl ester and unsaturated fatty acid methyl ester, which is significantly different from diesel, large-scale application of biodiesel is necessary. In-depth research on engine reliability, optimization of combustion and emissions, economics of production and use of biodiesel, and carbon dioxide emissions, there are still some key scientific issues to be addressed in the application of biodiesel to diesel engines:
(1) Nitrogen oxide control strategy for biodiesel engines: Biodiesel engines can significantly reduce CO, HC and PM emissions, but biodiesel emissions are usually caused by biodiesel molecules containing 12% oxygen.
The NOx emissions of the aircraft are about 10% to 12% higher than those of conventional diesel engines.
(2) Effects of physical properties of biodiesel on spray pattern, mixture formation and PM generation mechanism:
The viscosity of diesel is higher than that of commercial diesel. The compressibility of fuel is also significantly different from that of diesel. Thus, when biodiesel is directly applied to diesel engines, the fuel spray characteristics change significantly.
(3) Unconventional emissions from burning biodiesel engines: Although biodiesel can significantly reduce CO, PM and HC emissions, biodiesel contains a small amount of methanol (or ethanol), which is bound to occur during combustion. Various harmful unconventional emissions such as formaldehyde, acetaldehyde, olefins and alkynes.
(4) Particulate matter emissions from biodiesel engines: Biodiesel can reduce particulate matter emissions (mass), but the impact on the concentration of particulate matter remains to be further explored.
(5) Effect of micro-molecular structure of biodiesel on engine combustion emission characteristics: The molecular structure of different methyl esters in biodiesel includes carbon chain length, number of double bonds, and branched structure formed by different alcohol preparations influential .