Fuel Injection Scheme for a Compact Afterburner Without Flameholders

Abstract

State-of-the-art afterburners employ spray bars and flameholders to burn the fuel. Such afterburner designs significantly increase the length (and thus weight), pressure losses, and observability of the engine. This paper presents a feasibility study of a compact “prime and trigger” afterburner that eliminates the flameholders and, thus, eliminates the above-mentioned problems. In this concept, afterburner fuel is injected just upstream or in between the turbine stages. As the fuel travels through the turbine stages, it evaporates and mixes with the bulk flow without any significant heat release from combustion, a process referred to as “priming.” Downstream of the turbine stages, combustion is initiated either through autoignition or by using a low power plasma radical generator to “trigger” the combustion process. The prime and trigger injection and ignition scheme has been investigated using an experimental setup that simulates the operating conditions in a typical gas turbine engine. In this study, a trigger was not used and combustion of the fuel was initiated by autoignition. In a parallel effort, a physics-based theoretical model of the priming stage was developed in order to predict the location of fuel autoignition. The theoretical predictions and the experimental measurements of temperature and CH* chemiluminescence confirm the feasibility of the proposed prime and trigger concept by demonstrating the controlled autoignition of the afterburner fuel.