Aircraft industry tackles complexities of non-CO2 emission reductions

In June, results from the ECLIF3 study—conducted by Airbus, Rolls-Royce, Germany’s DLR aerospace research agency, and energy group Neste—revealed a 56% reduction in contrail-forming ice crystals from an A350 aircraft powered by unblended SAF. Simulations by DLR projected a 26% reduction in climate impact from contrails when using SAF instead of jet-A.

Timothy Snyder, Pratt & Whitney’s aerothermal chief engineer, noted that more accurate data from flight evaluations is now sought to assess factors such as contrail formation. “Now we are looking at the contributors to contrail formation,” Snyder explained. “These come from sulfur in fuel, incomplete combustion, and lubrication oils. What happens when these contributors are combined with the water-rich exhaust plume is what we are trying to understand.”

Improvements in combustor technology have already shown promise in reducing non-CO2 emissions. According to Pratt & Whitney, GTF engines currently in service have reduced NOx emissions by 50% and non-volatile particulate matter (nVPM) by more than 100-fold.

Pratt & Whitney plans further tests using a full annular combustor rig to measure emissions under inflight conditions. This data will help estimate reductions in contrails and validate them with inflight engine emissions data.

Meanwhile, Collins Aerospace is working on detecting ice super-saturation regions during flights to provide guidance on altitude adjustments that might avoid forming contrails. However, Snyder acknowledged that such changes might increase fuel burn and CO2 emissions.

Currently not assessed by the European Union’s Emissions Trading Scheme (ETS), some industry experts expect non-CO2 emissions regulations will soon change. Airline industry group IATA has issued a policy document on this issue while member carriers like Delta Air Lines have participated in pilot studies on emission avoidance.

4Air recently released a study assessing projected non-CO2 emission footprints within business aviation. According to 4Air president Kennedy Ricci: “Non CO2 emissions are down to where operators emit and in what conditions.” The study concluded that operational adjustments could significantly reduce overall non-CO2 impacts.

Modern business jets may be better suited for higher altitudes where contrail formation is less prevalent. As part of its work with private charter operator Flexjet on a contrail reduction pilot program, 4Air optimized flight paths based on contrail forecasts.

Ricci acknowledged trade-offs between different types of emissions but emphasized that future regulations would necessitate addressing these issues: “Regulations [for non-CO2 emissions] are coming so you are going to have to care about this.”