The thesis investigated carbonyl and hydrocarbon emissions from biodiesel blends with diesel or Α fuel. Different technologies were used to improve biodiesel combustion. Plasma was used to improve diesel–biodiesel combustion and improved swirl–stabilized fuel injectors were used to improve combustion from biodiesel–jet fuel. The diesel– biodiesel blended fuels′ combustion ⟨hydrocarbons and carbonyl compounds⟩ emissions were analyzed and interpreted for plasma on and plasma off conditions. Plasma assisted combustion ⟨PAC⟩ is known to improve fuel efficiency, enhance and stabilize combustion performance and enhance fuel reforming. Fuel–rich fuel⁄air mixture is introduced into a plasma field and further downstream, the secondary air is added resulting in overall fuel– lean condition mixture, and properly hold the flame inside the combustion chamber. It is found that the total hydrocarbons emission index ⟨EI⟩ & total carbonyls EI is lower for plasma on condition than for plasma off condition for a given fuel–air equivalence ratio ⟨Φ⟩. For plasma on, flame is sustained over a larger lean Φ than plasma off. The major carbonyls detected were acetone and acrolein.
Straight⁄ branched alkanes & methyl esters were the dominant hydrocarbons identified. The plasma′s thermal and kinetic effects helped in reducing the formation of incomplete oxidation products and extending the lean flammability limit; hence enhancing the overall combustion performance. Reduced hydrocarbons and carbonyls emissions from plasma can be used to further support the use of plasma as an environment friendly combustion technology even for viscous fuels like diesel and B20.
A swirl stabilized pilot nozzle ⟨in atmospheric rig⟩ and a low–emission Multi–nozzle lean direct injection ⟨MLDI⟩ combustor ⟨in pressurized rig⟩ was used to burn pure Α fuel as well as its blends with biodiesel ⟨BJ20 & BJ50⟩ to compare the emissions. The various aspects of this combustor design have the goal of reducing residence time, resulting in lower overall nitrogen dioxide formation by the thermal pathway. In atmospheric rig, biodiesel blends ⟨BJ20 & BJ50⟩ yielded less carbonyls and hydrocarbons emissions compared to Α fuel for fuel–rich conditions. For pressurized rig, as pressure across a single stage nozzle ⟨pilot⟩ was increased, total carbonyls EI and hydrocarbons EI decreased for both BJ20 and Α, for same mixed combustor temperature. The minimum value was recorded for highest power operating condition i.e. multi– stage nozzles. Α, however, tended to produce lesser hydrocarbons and carbonyls compared to BJ20. The main carbonyls identified were acetone, formaldehyde, acetaldehyde, benzaldehyde & acrolein while alkanes, hexa⁄ octadecanoic acids, tridecanol & methyl esters ⟨only observed for BJ20 in pressurized rig⟩ were the dominant hydrocarbons emitted. Excess unburned hydrocarbons may well be due to unsuitability of the small nozzles in this experiment for biodiesel blends.