Mitigation effects of alternative aviation fuels on non-volatile particulate matter emissions from aircraft gas turbine engines: A review

Global air transportation has grown rapidly in the past decade until the recent coronavirus pandemic. Previous research has demonstrated that particulate matter (PM) emissions from aircraft gas turbine engines can impair human health and environment, and may play a significant role in global climate change via direct absorption of solar radiation and indirect effect by their interaction with clouds. Using alternative aviation fuels (AAFs) from different sources have become a promising means to reduce aviation PM emissions and ensure energy sustainability. This work presents a review of non-volatile PM (nvPM) emission characteristics of aircraft gas turbine engines burning conventional aviation fuel (CAF) and CAF/AAF blends from recent ground and cruise tests. Current engine emission regulations, as well as available aviation PM emission prediction models and inventories are also discussed. Available nvPM emission characteristics, including particle number, particle mass, and particle size distribution (PSD), are analyzed and compared among different studies. The synthesized results indicate that burning AAFs tends to generate smaller size nvPM and reduce up to 90% nvPM number as well as 60–85% nvPM mass. The reduction is the most significant at low engine power settings, but becomes marginal at high engine power settings. The utilization of AAF blends reduces nvPM emission yet increases water vapor emission, which may promote contrail and even widespread cirrus cloud formation. Therefore, more investigation is required to quantify the potential impact of burning AAF at cruise altitudes on cloud formation and climate change. An appropriate estimation method for the particle number emissions from aircraft gas turbine engines fueled by both CAF and CAF/AAF blends is also in need aiming to establish a global aviation nvPM emission inventory and improve relevant global climate models.