Development of efficient high-temperature marine gas turbines (ship builder and marine enpaine-builder, sept., 1946)

Abstract

The oxidation resistance of turbine airfoils was enhanced by the use of diffused aluminides beginning in the mid-1950s; these coatings are still extensively used today. In the late 1960s, research began on developing overlay coatings which formed thin protective CrO2, SiO2 or Al2O3 scales on the coating surface. The Al2O3 scale forming coatings systems or MCrAlY coatings can operate at higher temperatures than other systems and can protect turbine airfoils for engines used in electric power generation, naval surface ship and aircraft propulsion, particularly in commercial and transport service.Most engine manufacturers agree that the best near-term candidate for major engine performance improvement would be to develop successfully thermal barrier coatings for turbine airfoil applications. Thermal barrier coatings could allow up to a 149°C (300°F) increase in turbine inlet temperature without a penalty in service life. Alternatively, at current operating conditions they could significantly extend engine hot-section life by reducing the airfoil operating temperature and eliminating hot-streaking problems.Diesel engines are the most fuel-efficient production heat engines yet devised. This level of performance has been achieved with very modest use of advanced materials. Thus, as far as performance improvements are dependent on materials, the diesel engine holds an exciting potential.The largest diesel performance gains in a decade have been achieved with turbocharging advancements. The major gains for the next decade appear to be in the low heat rejection engine concept, generally referred to as the “adiabatic diesel concept”. The major efficiency advances obtainable with the adiabatic diesel concept result from converting the increased exhaust gas energy into work. The most viable energy extraction method is to install another turbine in the exhaust that is mechanically connected to the engine output shaft. This is termed “turbocompounding”. The greatest improvement comes from a bottoming cycle. The problems of low heat rejection diesel engine waste heat utilization are cost, complexity and durability.