Two working papers studying Sustainable Aviation Fuels

1. Case Study on SAF Emissions from Air Travel considering Emissions Modeling Impact

In a world where aviation is a significant contributor to greenhouse gas emissions, exploring alternative fuels has become a key focus for reducing the environmental footprint of air travel. This case study dives into the emissions impact of Sustainable Aviation Fuels (SAF) compared to conventional aviation fuel, using a real-world flight trajectory from Stockholm, Sweden to Bordeaux, France, as the basis for analysis.

The study employs two methodologies to estimate emissions of hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) along the flight path. The first method, SF2, adapts Boeing Fuel Flow Method 2 for different fuel types and still uses emissions data of conventional fuels, while the second, EC-SF2, improves upon SF2 by incorporating SAF-specific emissions data.

Key findings reveal that SAF with higher calorific values increased HC and CO emissions but reduced NOx emissions when using SF2. Conversely, the EC-SF2 method, which adjusts both fuel flow and emissions indices for SAF, demonstrated a more consistent reduction across all emissions (Figure 1). This emphasizes the importance of using accurate methodologies when assessing SAF's environmental impact.

This research is part of the ongoing efforts to explore sustainable solutions for reducing the environmental impact of air travel, with a focus on improving emission calculation methods for SAF. It offers valuable insights into how SAF can support the aviation sector's transition toward greener operations.

Figure 1 Comparison of cumulative HC, CO, and NOx emissions of SAF relative to conventional fuel using SF2 and EC-SF2 methods.

2. Evaluating In-Flight Emission Indices Calculation Methods for Sustainable Aviation Fuels

This ongoing study aims to refine and improve existing methodologies for accurately calculating in-flight emissions of Sustainable Aviation Fuels (SAF). The focus is on modifying the Boeing Fuel Flow Method 2 (BFFM2) and the Mission Emissions Estimation Methodology (MEEM) to estimate the emissions of hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx), and non-volatile particulate matter (nvPM) for SAF, in addition to carbon dioxide (CO₂), water vapor (H₂O), sulfur dioxide (SO₂), and sulfate emissions, which are proportional to fuel consumption.

The proposed modifications to the BFFM2, presented in Figure 2, include the introduction of a precise fuel flow correction factor and the adjustment of sea-level emission indices through the application of correction factors derived from chemical kinetic modeling.

For nvPM emissions, the study focuses on refining the MEEM method by evaluating existing models as well as developing our own model, which is currently in progress, to estimate changes in nvPM emission indices when using SAF or their blends. This assessment ensures that SAF-specific characteristics are properly accounted for in emissions calculations. 

The study also plans to incorporate a case study using Flight Data Recorder (FDR) data to illustrate the impact of SAF on total emissions along a flight trajectory. By improving the accuracy of these methods, the research aims to support better environmental assessment strategies in aviation.

Figure 2 Process of the proposed SAF-modified BFFM2

Author: Evelyn Otero

Editor: Kyriaki Daskaloudi