Results and conclusions

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Via substitution of particle diameters ranging from 0.001 to 10μm into the previously described equations it is possible to generate deposition fractions for particle size ranges associated with PM, this is shown in Figure 2.27.

Exhausts particulates produced by gas turbine and automotive engines often exhibit high particle number concentrations in the 10 - 100nm (0.01 - 0.1µm) size range, a region that the ICRP deposition model predicts will have the highest deposition fraction in the alveolar region of the repository tract. As was mentioned in previous discussion, with regards to PM size and toxicity it is particles in this size range which possess the ability to access the deepest areas of the lungs and are currently of most concern to researchers.

Figure 2.27: Particle deposition fraction profiles for specific respiratory tract sections as described by the ICRP particle inhalation model.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

0.001 0.01 0.1 1 10

Deposition Fraction

Particle Diameter (μm)

Total Head Airway Tracheaobronchial Alveolar

Review of Gas Turbine and Automotive Engine Technologies and Exhaust Emissions

2.7 PM Regulations for Gas Turbine and Automotive Engines

Most emission regulations are now controlled by individual sector specific governing bodies which source direction from local or collaborating Governments. The governing body which publishes standards and recommended practises for the aviation industry is the ICAO. Specifically relating to the gas turbine PM emissions the ICAO defines regulatory standards and measurement requirements through ICAO Annex 16, Volume 2: Environmental Protection – Aircraft Engine Emissions publication [71].

In the automotive industry the leading body on particulate emissions is the UN-ECE GRPE (Working Party on Pollution and Energy) who implemented the PMP Working Group and the PMP Programme. The final results of these investigations were included in UN-ECE Regulation No.83 – Emissions of N¹ and M¹ vehicles [72]. The following sub-sections will discuss some notable aspects of both aviation and automotive PM regulation.

2.7.1 The LTO Cycle

To meet Annex 16 certification requirements, specific emission test points must be considered. The ‘Landing and Take-Off Cycle’ (LTO cycle) details the percentage of rated thrust an engine must produce, and for how long emissions sampling should occur at each specific thrust condition. Four conditions are considered, these being take-off, climb, approach and taxi, details of which as illustrated in Figure 2.28 and shown in Table 2.5.

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Figure 2.28: Illustration of ICAO exhaust emission certification procedure (LTO cycle), reproduced from www.icao.int.

Table 2.5: LTO cycle operating modes.

Operating mode Thrust setting (%) Time in operating mode (minutes)

Take-off 100 0.7

Climb 85 2.2

Approach 30 4

Taxi 7 26

The LTO cycle is intended to replicate the proportion of time an average commercial aircraft will spend at each of the listed engine conditions while completing the low altitude portion of a journey. It is worth highlighting that the main objection of the LTO cycle is to aid in the monitoring of PM emissions from a local air quality standpoint, as the entirety of these regulated emissions are released below 3000 feet. Currently there are no regulatory or measurement standards for cruise emissions occurring above 3000 feet primarily due to the sampling difficulty associated with taking in flight samples. It is however at cruise altitudes where the majority of exhaust emissions occur and thus this can create ambiguity when comparisons are made between short and long haul flights. Table 2.6 shows the percentage of total emissions associated with the LTO cycle criteria for a typical long and short flight.

Review of Gas Turbine and Automotive Engine Technologies and Exhaust Emissions

Table 2.6: LTO relevant emissions results from a long and short haul flight presented as a percentage of the total full journey emissions [73].

Exhaust Emissions (% of total journey emissions)

Fuel CO2 NOx

Short haul (London to Glasgow) 37 37 32 Long haul (Los Angeles to Tokyo) 3 3 2

Although a long haul flight will emit far greater total exhaust emissions, when looking at the LTO cycle in isolation it is the short haul trip which may appear to be more of a concern from a local air quality perspective.

2.7.2 SAE Smoke Number and Gaseous Emissions for Aviation Gas Turbines Smoke Number (SN) is a dimensionless value used to quantify solid PM emission and is the current regulatory standard for aviation gas turbine engine exhaust smoke measurement. It is defined by the SAE ARP1179D [74] and is determined by the relative reflectance of a standard filter paper following exposure to the engine exhaust in question, under set experimental conditions. SN is rated on a scale of 1 to 100 where higher smoke densities produce larger SN ratings.

The measurement procedure for determining SN involves first calibrating a reflectometer using a coloured tile of known reflectance. The reflectance of each sample filter paper, manufactured by Whatman Ltd (size No. 4), is then recorded prior to use to give an absolute reflectance of the clean filter material, Rw. A filter which has been inserted into a holder of defined geometry is then exposed to a sample flow of 14L/min ±0.5L/min for sufficient time (no less than 1 min) that a fully charged representative sample is achieved. Consecutive samples must be taken at each measurement condition, at which 16.2 kg/m² ±0.7 kg/m² of exhaust gas must passed through each filter, until at least 3 samples are obtained which agree within ±3 smoke

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exhaust gas/m² of filter paper. A stained filter is then retested using the reflectometer to achieve an absolute reflectance of the sample spot, Rs. The smoke number of an individual exhaust sample (SN’) can then be found [74]:

𝑆𝑁^′ = 100[1 − ^𝑅𝑠

𝑅𝑤 ]