Carbon Brainprint Case Study: ceramic coatings for jet engine turbine blades

摘要

Ceramic thermal barrier coatings (TBCs) are applied to jet turbine blades toprotect them from the high temperature gases leaving the combustion chamber andto increase the efficiency of the engine. Professor John Nicholls of the SurfaceScience and Engineering Group, Cranfield University has been working with Rolls-Royce plc for about 17 years to improve the insulating performance of TBCs. As aresult, the TBCs used in the current generation of aircraft turbofan jet enginesachieve a temperature drop about 80ºC greater than at the start of the work,with an estimated fuel saving of about 1%.This case study considered two engine types: Trent 700, used on about half theAirbus A330 aircraft currently in service, and Trent 500, used on all AirbusA340-500 and A360-600 aircraft. The greenhouse gas emissions considered were, inorder of magnitude, carbon dioxide from combustion of the fuel, emissions duringextraction and refining of the fuel, and emissions of other greenhouse gasesduring combustion. Emissions associated with transport of the fuel were found tobe negligible compared with these, and all emissions not related to fuelconsumption, for example manufacture of the coating, were also assumed to beinsignificant or excluded from the assessment because they were unaffected bythe change in the TBC.The baseline fuel consumption during each flight phase (landing and take-offcycle and cruise) was estimated from publicly available data. Airline activitydata for A330 and A340 models from European operators was taken to representtypical patterns of use, enabling annual emissions per aircraft to becalculated. Data on current operating aircraft and orders were then used toestimate the total current and projected future emissions. From these, thehigher emissions that would have occurred in the past if the improved TBCs hadnot been used, and the corresponding future emissions, were estimated.The best estimates of the current emissions (the retrospective brainprint) forindividual aircraft were 1016, 1574 and 1646t CO2e/year for A330, A340-500 andA340-600 respectively, giving 568 kt CO2e/year for the total fleet. Includingall the aircraft on order, the prospective emissions reduction was 833kt CO2e/year. Assuming a service life of 20 years, the total brainprint wasapproximately 17MtCO2e.An uncertainty analysis was performed with assumed uncertainties for aircraftactivity, fuel consumption and the efficiency change. The 95% confidenceinterval for the current annual emissions reduction was 429-721kt CO2e/yearexcluding the efficiency change uncertainty, and 258-1105 if it was included.The relative changes in the other output measures were similar. Assuming thatolder engines do not and will not benefit from the improvement, reduced thetotal brainprint to 14MtCO2e. The assessment did not include an adjustment forthe effect of emissions at high altitude, which would increase all the outputsby a factor of 1.9.