Experimental Results of Hot Section Metal Temperature Measurements of Rolls-Royce Allison 501KH Under Massive Steam Injection

Abstract

It has always been thought by the gas turbine industry that steam injection will shorten the effective life of certain gas turbine parts. Recently it was shown that a number of steam injected Cheng Cycle Rolls-Royce Allison 501KH gas turbines, accumulated more than 2.5 million logged hours of operation and with a prolonged parts life. The “hot parts” of a Rolls-Royce Allison 501KH gas turbine engine that are of concern, are the first stage nozzle, the first stage blade, and the second stage nozzle. These parts are all air cooled through the first stages internal passages. (The second stage blades and on down are not internally cooled.) The concern raised in many gas turbine institutions is that the metal temperatures of these hot parts, due to the heat conductivity properties of injected steam, will make them deteriorate faster. An experiment was completed using a steam injected Cheng Cycle, on an Allison 501KH gas turbine engine. In the experiment, a substantial number of thermocouples were attached to the surfaces of the turbines hot parts. This engine had a steam injection rate of up to 18% airflow. The experimental results showed that if steam could be properly mixed with the cooling air before the air enters into the cooling passages of the hot parts, the metal temperatures did not increase. During the operation of the engines, it was recorded that the hot parts lifetime increased from 25,000 hours before the hot parts section had to be overhauled, to 42,000 hours (on average) before they needed to be overhauled. This paper will report the measurement installation in detail. The results before and after steam injection in the hot parts sections of the Rolls-Royce Allison 501KH engine will also be discussed.