Session: 01-03 Advanced Engine Components and Future Propulsion Systems

Paper Number: 191623

191623 - Piston Optimization for Improving Low-Cetane (Cn25) Fuel Capability of Fuel-Flexible Aviation Ci Engines 

Abstract: 

Extending the operability of aviation compression-ignition (CI) engines to low-cetane fuels like CN25 is crucial for achieving fuel-flexible combustion across a wide range of cetane numbers (CNs). However, at altitude conditions, the combination of low ambient temperature and pressure, along with the inherently low reactivity of CN25, leads to delayed start of combustion (SOC) and unstable ignition behavior. In aviation applications, maintaining stable, reliable combustion is essential for engine reliability and performance. This study examines piston bowl optimization as a strategy to improve combustion stability and ignition behavior of CN25 in an aviation CI engine operating at altitude. Three piston geometries, stock, wave, and wave+offset, were tested using CONVERGE CFD simulations with split pilot–main injections, keeping total fueling at 12 mg, while varying the pilot mass (3, 4, and 5 mg). Results show that the wave+offset piston consistently advances SOC and enhances ignition coupling due to its inclined, laterally offset bowl configuration, which directs pilot combustion products toward the centrally mounted injector. This promotes better mixing, creates multiple ignition sites, and favorable local turbulence levels. Conversely, the wave piston experiences an SOC delay at high pilot fueling (5 mg) due to excessive mixing, which disperses ignition kernels away from high-temperature regions. Overall, the wave+offset piston offers superior mixture stratification, ignition kernel robustness, and heat-release behavior, making it the most effective design for stabilizing CN25 combustion under high-altitude aviation conditions and enabling greater fuel flexibility in CI engines.

Presenting Author: Vasudev Chaudhari University of Wisconsin Madison

Presenting Author Biography: Vasudev Chaudhari is a Scientist I specializing in engine combustion, alternative fuels, and CFD modeling. With over five years of post‑PhD experience in India and the U.S., he works on fuel‑flexible engines and simulations using CONVERGE and GT‑SUITE.

Authors:

Vasudev Chaudhari University of Wisconsin Madison
Randy Hessel University of Wisconsin-Madison
Aneesh Kale University of Wisconsin–Madison
Kenneth Kim US Army DEVCOM Army Research Laboratory
Chol-Bum M. Kweon US Army DEVCOM Army Research Laboratory
Sage Kokjohn University of Wisconsin–Madison