Fuel Savings Policies Via Engine Efficient Operations

We can’t deny World has changed, and so our Industry. Probably more severely impacted than any other one.

With the progressive aircraft fleets re-entry into service –on August 11th, as per EUROCONTROL, Europe accounts 52% less operations year on year comparison- it becomes more important than ever any single possible € that can be saved.

There are dozens, to not say hundreds, of improvement actions that can be undertaken, by keeping the levels of operational reliability and safety. I address in this article a set of feasible measures aimed to have under control fuel consumption via engine efficient operations. More precisely particularized to my area of expertise: ATR Aircraft – PW100 engines fleet. Because every drop of fuel wasted counts.

Turboprop aircrafts, in general, are more efficient for regional routes. In the range of the regional market, mainly between 200 to 400NM, turboprop fleets provide no significant flight time differences compared to turbojets, but offering the best trade-off between fuel burned and speed. As an average fuel consumption per passenger for distances of 200NM (65% Load Factor) accounts approximately 7 US Gallon for a Jet Aircraft vs 4 US Gallon for a Turboprop.

Degradation makes engine thermodynamic cycle yield to be reduced. During normal operations all engines, due to its regular degradation, will experience rubbing, thermal stress, mechanical stress, dirt accumulation, FOD ingestion or gas path leaks among others issues. These effects will result in non-desirable and measurable decrease of engine performances, mainly lead by:

·      ITT/T6 (Turbine Temperature) increase

·      SFC (Specific Fuel Consumption) increase.

A smart Engine Fleet Management activities have to embrace a comprehensive plan to react against SFC raise at different levels:

1 - Shop visits to restore engine performances

This is probable a too drastic measure to exclusively restore SFC, and engine removals are driven by total different reasons. However, among other operations, all these actions can improve engine efficiency and restore SFC close to previous levels. The goal is to set the most convenient workscope for each engine at each time, also taking in to account fuel burn reduction considerations.

Therefore SFC is reduced once engine is repaired at shop by:

·      Re-establishing tip clearances.

·      Internal seals replacement

·      Mechanical components fixing-up

·      Combustion chamber overhaul

·      Cold section area local repairs (damages rectification)

2 - Line maintenance activities to mitigate SFC increase

2.1 - Engine washing Program

A common practice to improve engine in-service efficiency is to desalinate and wash the engine. Regular washes have the purpose to remove dirt, contaminants and deposits at different engine gas path areas, thus enabling reduce the fuel burned.

Engine washing program is a key element on day-to-day SFC control. Depending on the severity of the environmental conditions and operational constraints on ground, each airline should identify their most convenient intervals and re-evaluate them with in-service experience. Engine washing program compliance is a requirement on most Engine Maintenance Programs, having a critical effect on both SFC and aerodynamic surfaces corrosion control.

2.2 - Line Maintenance defects correction

FODs actually impact gas path performance, and consequently SFC. The majority of the engines allow, up to certain limits, the blend repair of compressor aerodynamic surfaces with the engine installed on-wing. Recurrent inspections via borescope ports and subsequent blend repair completed when defects are found, further to the airworthiness requirements to do so, also has a positive effect on engine efficiency and subsequently restoring SFC levels up to certain limit.

 2.3 - Engine Health Monitoring

Engine Health Monitoring tools, further to their main purpose enabling to follow an Engine On-Condition Maintenance Program, also facilitate and point in-service fuel wasting sources. Problems which can be identified and fixed in a much efficient and swift way when you can get the most from your Engine Condition Trend Monitoring.

·      Best moments to plan Performance Recovery Washes

·      Problems in the cold section as bleed valves malfunction, diffusor leakages or presence of FOD. These kind of problems significantly increase SFC. If detected at early stage, where only ECTM sensitivity is able to identify them, significant amount of fuel over-wasted can be saved.

·      Fuel Flow indication discrepancies

·      Problems at fuel nozzles level

3 - Operational tips at engine level to reduce fuel burned

 A batch of operational tips aimed to reduced unnecessary fuel consumption are here enumerated:

·      Ensure aircraft BLEED OFF during engine start and take-off operations. It has a remarkable positive effect in decrease engine ITT and fuel burned.

·      Judicious use of reverse based on limited landing runway length. Minimize use of engine reverse significantly reduces fuel consumption. This is always subject to landing conditions.

·      Cool down engine 2 minutes before shutdown. This procedure reduces the level of fuel nozzle coking, therefore extends its life. It also reduces oil cocking build up which in turn has a positive effect to keep rotary elements efficiency.

·      Minimize Hotel Mode operations. In Hotel Mode fuel consumption is by 110Kg/Hr. Use of GPU when available is always preferred.

To sum up

To work wisely at different levels at the engine and endorsing some of these measures, this can bring in turn appreciable amounts of fuel quantity saving. Fuel represent the first source of airline Direct and Indirect Operating Costs, accounting for circa 25%-35% depending on the operator. So any little save on fuel consumption can have an appreciable effect on airline P&L.

A day-to-day representative example

Based on my experience with PW100 engines, and operational data that I have been analysing for years: Considering a scenario of a typical regional flight by 300NM (≈1:15Fh), we can estimate a fuel consumption around 450Kg per engine when using one powerplant with dirt impellers and air bleed issues.

Exactly the same operation done with a clean compressor engine, and with its bleed system working correctly could represent at least 15Kg less fuel burned:

·      ≈ -1.3% clean compressor

·      ≈ -2% bleed problems fixed

On a typical regional airline where each aircraft is flying an average of 6 revenue flights per day, this could represent by 1300Kg of fuel over-wasted in a week per aircraft, if dirt impellers are not washed and bleed issues are not detected via Engine Condition Trend Monitoring and rectified at early stage!

Should you have any comments or questions, or you would require any assistance with PW100 Fleet Management, do not hesitate send me a message.

I?aki Azcoitia – Senior Fleet Manager - www.rcpexperts.com

References

-PW100 operational data 2013-2020

-Parametric Specific Fuel Consumption Analysis of the PW120A Turboprop Engine . Specific Range Solutions Ltd.

-Fuel Saving - Contribuiting to a sustainable air transport development. ATR, 2011