Gas Turbine Engine Emissions—Part II: Chemical Properties of Particulate Matter

Abstract

The characterization of volatile and nonvolatile particle materials present in gas turbine exhaust is critical for accurate estimation of the potential impacts of airport activities on local air quality, atmospheric processes, and climate change. Two field campaigns were performed to collect an extensive set of particle and gaseous emission data for on-wing gas turbine engines. The tests included CFM56, RB211-535E4-B, AE3007, PW4158, and CJ610 engines, providing the opportunity to compare emissions from a wide range of engine technologies. Here we report mass, number, composition, and size data for the nonvolatile (soot) and volatile particles present in engine exhaust. For all engines, soot emissions (EIm-soot) are greater at climbout (85% power) and takeoff (100%) power than idle (4% or 7%) and approach (30%). At the engine exit plane, soot is the only type of particle detected. For exhaust sampled downwind (15–50 m) and diluted by ambient air, total particle number emissions (EIn-total) increases by about one or two orders of magnitude relative to the engine exit plane, and the increase is driven by volatile particles that have freshly nucleated in the cooling exhaust gas both in the free atmosphere and in the extractive sample lines. Fuel sulfur content is the determining factor for nucleation of new particles in the cooling exhaust gases. Compositional analysis indicates that the volatile particles consist of sulfate and organic materials (EIm-sulfate and EIm-organic). We estimate a lower bound S[IV] to S[VI] conversion efficiency of (0.08±0.01)%, independent of engine technology. Measurements of EIm-organic ranged from about 0.1 mg kg−1 to 40 mg kg−1. Lubrication oil was present in particles emitted by all engines and accounted for over 90% of the particulate organic mass under some conditions. The products of incomplete combustion are a likely source of the remaining volatile organic particle material.

Composition and Sources of the Organic Particle Emissions from Aircraft Engines

“…Partly because the knowledge base was limited and partly due to the potential impacts, particular emphasis has been placed on characterizing turbine engine PM emissions. Recent studies confirm that gas turbine PM is composed of nonvolatile soot particles and volatile materials, themselves consisting primarily of sulfate and organic components Timko et al 2010bTimko et al , 2013. Here, the term "volatile" refers to its vapor state at the elevated temperatures of the engine exit plane (>500 K).…”

“…Here, the term "volatile" refers to its vapor state at the elevated temperatures of the engine exit plane (>500 K). By mass, volatile PM can dominate PM emissions during low power operation, during operation at low ambient temperature (<275 K), and/or for combustion of high sulfur fuels (Timko et al 2010b(Timko et al , 2013. Depending on conditions and engine technology, the volatile PM can coat existing soot particles, enter a nucleation/growth mode, or exist as a separate size mode (Timko et al 2013).…”

“…Motivated by these environmental concerns, researchers have performed studies to advance the current state of knowledge of gas turbine engine NO X Wormhoudt et al 2007;Wood et al 2008;Timko et al 2010a; Lee et al 2011;Santoni et al 2011), volatile organic compounds (Spicer et al 1994;Herndon et al 2006Herndon et al , 2009Knighton et al 2007;Yelvington et al 2007;Timko et al 2010c;Beyersdorf et al 2012), and PM emissions (Herndon et al 2005bLobo et al 2007Lobo et al , 2011Hagen et al 2009;Onasch et al 2009;Bulzan et al 2010;Timko et al 2010b). Partly because the knowledge base was limited and partly due to the potential impacts, particular emphasis has been placed on characterizing turbine engine PM emissions.…”

Updated Correlation Between Aircraft Smoke Number and Black Carbon Concentration

“…The OC consists of products of incomplete combustion of fuel and lubrication oil, while emissions of sulfate result from the conversion of fuel sulfur compounds (Timko et al 2010;Kinsey et al 2011). EI(BC) is generally an order of magnitude greater than the emission index of OC and sulfate for high engine thrust settings when exhaust is sampled at the engine exit plane.…”

“…This method is routinely used to estimate the public health impacts of aircraft LTO PM emissions in the United States (Ratliff et al 2009;CSSI Inc. 2010;Arunachalam et al 2011;Levy et al 2011;Woody et al 2011). While several studies have measured the mass of emitted BC per unit fuel burned, known as EI(BC), the majority of engines in service have not been measured and for these the SN remains the only measure of their PM emissions (Timko et al 2010). Research efforts to define a standard procedure to measure aircraft nonvolatile particle number and mass emissions are ongoing (SAE 2009) but no plans exist to measure engines currently in service.…”