Investigation of the sooting propensity of aviation fuel mixtures

Abstract

Aromatic compounds occurring naturally in jet fuels are precursors for the formation of soot in the exhaust gas of jet engines. Directly emitted in cruising altitude, soot particles lead to the formation of contrails and clouds influencing the radiation balance of the atmosphere. Hence, a detailed knowledge on the effect of aromatics on the sooting behavior is of great importance, especially for the development of alternative synthetic jet fuels. Investigations on the sooting propensity influenced by the molecular structure and concentration of diverse aromatic compounds contained in synthetic and fossil aviation fuels as well as blends of synthetic paraffinic kerosene (SPK) with aromatic compounds (SKA) were carried out experimentally. Using a predefined SPK fuel, five different blends—each containing a single aromatic compound—were prepared in addition to one blend with a typical composition consisting of all these aromatic compounds. In subsequent measurements, the concentration of the aromatics was increased from initially 8.0 vol%, to about 16.5, and 25.0 vol%. The aromatics added were toluene, n­-propylbenzene, indane, 1­methylnaphthalene, and biphenyl. The studied jet fuels include fossil-based Jet A-1 as well as different synthetic jet fuels (with and without aromatics). Furthermore, the experimental results of the sooting propensity are compared with the results of the hydrogen deficiency model being a measure for the amount of cyclic and unsaturated molecular structures occurring in a hydrocarbon fuel. This study shows the hydrogen deficiency as a useful tool to make predictions about the sooting behavior of different fuels compared to a reference fuel at a specified condition. Additionally, it is observed from the measured sooting propensities as well as from the model predictions of hydrogen deficiency that the structure of aromatic compounds presents greater influence on the soot formation than the aromatic concentration.

Influence of Oxymethylene Ethers (OMEn) in Mixtures with a Diesel Surrogate

“…The experimental set-up for the measurement of the sooting propensity is shown in Figure 2 and consists of four parts: (I) The preparation of the fuel-air mixture; (II) the burner; (III) the sampling probe; and (IV) the particle detection unit. The determination of the sooting propensity has already been previously described [13,14], so only a short description is given here. For the preparation of the fuel-air mixture (I), the liquid fuel is vaporized using a HPLC-pump (LC-20AD, Shimadzu) to feed the vaporizer [15].…”

Thermal cyclodimerization of isoprene for the production of high-performance sustainable aviation fuel

“…However, aromatic compounds also exhibit lower gravimetric net heats of combustion (NHOC) and are more prone to incomplete combustion and particulate emissions. [9][10][11] Recent work has also shown that many cycloalkanes can effectively swell legacy nitrile rubber o-rings, [6][7][8] while nearly all synthetic kerosenes are compatible with modern fluorosilicone or Vitont-based engine seals.…”

“…The elimination of aromatic compounds results in a number of enhanced properties including increased gravimetric NHOC, improved combustion properties, and reduced particulate formation. [9][10][11] To realize these optimized blends, efficient routes for the production of bio-based cycloalkanes are required.…”

A comparison between fossil and synthetic kerosene flames from the perspective of soot emissions in a swirl spray RQL burner

“…Soot emissions were correlated with the hydrogen content of the fuel, and soot reductions were achieved in the fuel with low aromatic content while increased soot emissions were detected for the alternative fuel with higher aromatic content and lower hydrogen content [25]. Richter et al [26] also looked at the aromatic content of different synthetic fuels and compared them to the traditional Jet A-1 fuel. They showed that hydrogen deficiency of the fuel is a good measure for sooting behaviour.…”

“…They showed that hydrogen deficiency of the fuel is a good measure for sooting behaviour. Additionally, they revealed that the aromatics structure in the fuel plays a greater role in soot formation rather than its concentration [26].…”