High temperature, oxidation resistant, silicon nitride, ignition-assisted devices in multifuel aviation engines

Numkiatsakul, Prapassorn

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https://hdl.handle.net/2142/129867 Copy

Description

Title

High temperature, oxidation resistant, silicon nitride, ignition-assisted devices in multifuel aviation engines

Author(s)

Numkiatsakul, Prapassorn

Issue Date

2025-07-14

Director of Research (if dissertation) or Advisor (if thesis)

Kriven, Waltraud M.

Doctoral Committee Chair(s)

Kriven, Waltraud M.

Committee Member(s)

• Lee, Tonghun
• Shoemaker, Daniel P.
• Zuo, Jian-Min
• Kim, Kenneth S.

Department of Study

Materials Science & Engineerng

Discipline

Materials Science & Engr

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Oxidation Resistance
• Silicon Nitride
• Ceramic Glow Plugs
• Ignition Assistance
• Degradation
• SiAlON
• High-Temperature Materials

Abstract

Recent advancements in aviation engine design have increasingly emphasized the use of lower-quality alternative fuels to diversify fuel sources, particularly for aircraft operating in remote or fuel-limited environments. However, many of these fuels exhibit low autoignition reactivity, requiring supplemental thermal energy to initiate and sustain stable combustion. As a result, the development of multi-fuel engine technology has created a demand for robust ceramic heaters or Ignition Assisted (IA) devices capable of delivering consistent thermal input while withstanding the extreme conditions of high-temperature combustion environments. Silicon nitride-based glow plugs, commonly used as heaters in diesel automotive engines, were investigated as potential candidates for this application. These devices could rapidly reach surface temperatures of up to 1350 °C. However, they were originally developed for short-term operation in ground vehicles, primarily to assist combustion during cold starts. In contrast, ignition-assisted devices for multi-fuel aviation engines were required to operate continuously throughout an entire flight and maintain surface temperatures above 1100 °C, even under high-altitude cooling effects. No commercial device existed that fulfilled these requirements, which prompted the work presented in this dissertation. The core challenge in developing a reliable IA device was identified as a materials limitation. Specifically, the focus was placed on understanding the performance constraints and failure modes of silicon nitride-based systems (Si₃N₄), which serve as the primary structural ceramic in glow plug components. This research was divided into two parts. The first part involved a systematic characterization of commercial off-the-shelf glow plugs to evaluate their structural design, material composition, and failure behavior under engine-relevant conditions. Multiple degradation mechanisms were identified, including thermal cracking, interfacial delamination, sintering aid migration, and progressive oxidation. Glow plugs with U-shaped designs were particularly prone to delamination caused by thermal stress and electric-field-induced ion migration. Co-annular glow plug architectures, on the other hand, were more susceptible to oxidation-related degradation due to direct exposure of the heating elements to high-temperature oxidative environments. The second part of the study focused on addressing these degradation mechanisms - particularly oxidation - by developing improved ceramic materials. Three strategies were explored. The first approach involved incorporating aluminum nitride (AlN) as a bulk additive, which enhanced oxidation resistance by forming dense, protective, oxide layers. However, this approach introduced challenges related to reduced thermal conductivity and poor sinterability. The second strategy applied CaO surface treatments to sintered Si₃N₄ pellets, which promoted the formation of crystalline Ca-Mg-silicate phases to stabilize the oxidation front. These stable surface layers reduced oxygen ingress without altering the bulk microstructure. The third and most comprehensive strategy involved designing adjacent material systems, specifically O-SiAlON ceramics, synthesized via reaction sintering. These materials exhibited superior oxidation resistance when fabricated under carefully controlled conditions. Detailed analysis of O-SiAlON microstructure and composition provided insights into oxidation kinetics in sintered ceramics containing additives. The study revealed that oxidation resistance was governed by kinetics and oxygen transport through the microstructure. Samples with optimized grain structure and stable glassy phase composition showed the highest oxidation resistance. Phase evolution and oxidation behavior of O-SiAlON were found to depend strongly on sintering temperature and Al-O substitution level (x-value). Samples with moderate substitution levels (x = 0.1-0.2), sintered at 1550 °C, developed fine-grained, dense microstructures and stable protective phases with minimal glass volatilization, resulting in excellent oxidation performance. Overall, this dissertation presented a critical evaluation of the limitations of current IA ceramic materials and outlined promising strategies for improvement. The findings supported the potential of tailored silicon nitride-based compositions, surface engineering techniques, and alternative systems such as O-SiAlON to enable the development of reliable materials for ignition-assisted devices operating in multi-fuel, high-temperature combustion environments.

Graduation Semester

2025-08

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/129867

Copyright and License Information

Copyright 2025 Prapassorn Numkiatsakul

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