1. PPL-IR Europe Piston Engine Management for IR Pilots

2. Refresher: the classic four-stroke cycle INTAKE: intake valve open, piston pulled down COMPRESSION: valves closed, piston driven up POWER: valves closed, piston pushed down by expanding charge EXHAUST: exhaust valve open, piston driven up

3. Refresher: the classic four-stroke cycle compressing a gas heats it up expanding a gas cools it down

4. intake port on right, exhaust port on left this is a liquid cooled engine with dual overhead camshafts Note the non-linear movement of the piston near TDC and BTC

5. around TDC piston moves very little during about 20 deg either side of TDC pressure pulse too early = mechanical disadvantage

6. Pressure in cylinder during each of the four strokes. As pilot we can influence the yellow area by use of MP, RPM, mixture one full four-stroke cycle, two engine revolutions

7. Aluminium alloy looses 50% of its strength at 400 F.

8. Your cylinder heads are made of Aluminium alloy.

9. During certification the engine manufacturer uses individually controlled air ducts for each cylinder to 'show' the certificating authority that its engine will operate safely at redline CHT (for short durations and full rich)

10. In a practical airplane, the cooling of the cylinders will be less efficient than on the special engine test stand of the engine manufacturer. Engine baffling in aircraft installations runs from acceptable to horrible. Usually baffling doesn't improve with aging. In real life the owner/pilot is concerned about engine life and reliability. We can see that 400 F is the practical limit for CHT, while 380 F is the 'start thinking to do something' voluntary limit.

11. Here is what Lycoming has to say about CHT: (Piper Malibu Mirage) Quote: “Recommended cruise at 65% power, corresponds to 2400 RPM, 29 ” MAP. Lean to 1650 degree TIT or operate 100 degrees rich of peak TIT, whichever is less. For optimum service life, CHT’s in cruise should be maintained below 400 degrees. Regardless what power setting is used, cruise CHT’s should not exceed 435 degrees.” End of quote.

12. Stoichiometric mixture: every fuel molecule finds one oxygen molecule to burn

13. Stoichiometric mixture: every fuel molecule has the potential to find one oxygen molecule to burn PEAK EGT coincides with STOICHIOMETRIC MIXTURE FUEL = OXYGEN

14. Rich mixture: there are more fuel molecules than oxygen molecules

15. FUEL > OXYGEN RICH MIXTURE is any mixture with more FUEL than stoichiometric

16. Lean mixture: there are more oxygen molecules than fuel molecules

17. FUEL < OXYGEN LEAN MIXTURE is any mixture with less FUEL than stoichiometric

18. Both VERY RICH and LEAN mixtures burn SLOWER than stoichiometric

19. on current engines ignition is fixed at about 20-22 deg BTC compromise for full rich, take-off power, compromise for cruise power. sparkTDCPeak Pressure Pulse

20. making the mixture MUCH RICHER or LEANER will result in slower burning charge. Peak Pressure Pulse Top Center

21. Peak Pressure Pulse Top Center making the mixture MUCH RICHER or LEANER will result in slower burning charge. Peak Pressure Pulse will fall later after TDC giving more mechanical advantage.

22. making the mixture MUCH RICHER or LEANER will result in slower burning charge. Peak Pressure Pulse will fall later after TDC giving more mechanical advantage. Because a later PPP will fall further in the expansion part of the piston movement, the temperatures will be lower

23. Duration of a cycle is fixed and determined by RPM lower RPM give longer cycle at 2700 RPM 11,1 milliseconds at 2100 RPM 14,3 milliseconds

24. Duration of a combustion event (from spark to peak pressure) is variable and determined by mixture and other factors, not by RPM.. lean mixture burns slower and places the peak pressure later.

25. More factors influencing the burn rate of the charge besides mixture: Octane rating of fuel (Jet Fuel instead of Avgas), failure of single spark plug in cylinder (slower burning single flamefront) detonation !! (uncontrolled explosion: too early) pre-ignition !! (glow plug: too early)

26. an ideal ignition system would adjust the spark advance to let the Peak Pressure Pulse fall at the optimum position ( about 16 deg ATC) under all circumstances.

27. the only practical way to get this ideal ignition system to work is to measure the timing of the Peak Cylinder Pressure (ideally 16°ATC) inside the cylinder and adjust the timing of the spark.

28. From engine test stand: Same horsepower at ROP and LOP setting, LOP trace is smoother, (less peak pressure) cooler (farther from TDC + less peak pressure) more efficient (more mechanical advantage)

29. Classic engine curve, MIXTURE versus EGT/CHT/BHP/BSFC

30. EGT is a phony temperature, only useful for navigating the mixture curve

31. CHT is a real temperature and a direct reflection of internal cylinder pressures

32. as a pilot you are concerned with the Mixture control knob (Fuel flow) and its relation to EGT (fast reading navigation)

33. if you want to limit CHT to 400°F (RED BOX) or less, options are limited. Hottest CHT is at about 40°F ROP. Hottest exhaust valve temp is about 25°F ROP.

34. Hottest CHT is at about 40F ROP. Hottest exhaust valve temp is about 25F ROP. You don't want to run your engine between the magenta and orange arrows!

35. Why do the manufacturers recommend 50°F ROP as a cruise setting? Mystery?

36. To run 'properly' ROP would be about 100°F ROP, cutting very seriously in the published range numbers. (Marketing says NO) To run smoothly LOP would be impossible in most out-of-the-box engines without aftermarket engine analyser and injectors. (Marketing says NO) So, 50°F ROP is what the marketing dept wants, nobody else does.

37. Horsepower curve (BHP) is fairly flat ROP, but falls off rapidly LOP.

38. Best power falls at about 80F ROP but with high CHT

39. Best Economy falls at 20° LOP (low power) to 90° LOP (high power) but with power loss

40. Peak EGT to just LOP is a correct cruise power setting for moderate power.

41. 10-20F LOP is a very good cruise power setting for moderate power avoiding the power loss but with lower temps and good economy.

42. EGT is popular because it is fast-reacting, fairly easy to instrument. EGT has no limits, it is an artificial temperature.

43. On most turbocharged engines, Turbine Inlet Temperature (TIT) may be installed in place of /or combined with EGT. TIT does have a limit:: it is to protect the turbocharger from blade creep. At high power settings, TIT limit may be reached, run richer or leaner. The TIT limit is a long-term limit; it would not matter to run at or above the limit just for short periods during mixture adjustment.

44. Advantages of LOP mixture settings: safety advantages: Absolutely no CarbonMonoxide is formed, combustion is complete. Less stress on engine because of lower ICP and later power pulse. Almost 15-20% fuel savings in some cases. Extend range and/or payload for missions. intellectual advantages: Gives pilot more options and far better understanding of his engine. maintenance advantages: Less oil consumption because of lower blow-by by the rings caused by lower peak pressures. Cooler and cleaner running engine (less spark plug fouling). Instant troubleshooting on lots of ignition/valve problems. Oil stays cleaner longer. Spark plugs stay cleaner longer.

45. Disadvantages of LOP mixture settings; Some intellectual effort required. Some instrumentation required. Slight speed loss, probably 3 KTS or less (made good by increased range). Engine will probably need some fine-tuning (ignition, induction, injection). Fuel/Air ratios need to be balanced to run smoothly LOP.

46. Steps to make a conforming fuel-injected engine run smooth LOP: Very few engines will run smoothly LOP out of the box. The BHP curve is fairly flat ROP and drops off LOP. If one cylinder gets more fuel than the next one it will develop more power. Unless the fuel/air ratios are balanced, smooth LOP running will not be possible. To be balanced, all cylinders should reach peak EGT at the same fuel flow. The absolute EGT value at which a cylinder peaks is unimportant.

47. First step : fly the lean test. On autopilot, with safety pilot on lookout, set up cruise at medium power, ROP, preferably on a sector where you won't be disturbed for 15 minutes. Engine analyser required. 1. For a given fuel flow, write down EGT / CHT for each cylinder 2. slowly lean on fuel flow meter by 1 LPH or 0.2 GPH increments 3. allow to stabilize for about one minute 4. repeat step 1. until engine runs rough Notes: always go from rich to lean do not reverse if overshot. set your analyser to single digit readout if you have data recording capability in your engine analyser, just do a slow mixture sweep, the data is recorded every 6 seconds.

48. Second step: balance your F/A ratios: plot and evaluate the results. Using a spreadsheet, for each fuel flow value, enter EGT/CHT for each cylinder. Identify the peak EGT point per cylinder column and corresponding fuel flow. If all peaks fall within 1 LPH or 0.3 GPH you will have a smooth engine LOP because all cylinders will be developing same power. If the spread is larger, balancing work will have to be done on the injectors, induction air leaks may have to be fixed, ignition system may have to be looked at..

49. Third step: optimize your ignition system Test your ignition system with an in-flight mag-check LOP. Switch off one magneto at a time in flight, note that all EGTs rise; if not, you have a problem in that cylinder. When LOP the charge is harder to ignite and spark plugs, magnetos and harness need to be perfect. The in-flight mag-check will reveal weaknesses that would go undetected in a ground mag-check or in a spark plug 'bomb' test.. Expect 1 in 10 brand new spark plugs to fail the test out-of-the-box.

50. Points to watch when optimizing engine for smooth LOP running: -induction tubing rubber couplings -fuel drains in induction tubes Injectors spray fuel mist from top of cylinder into intake port. Some of this fuel-laden mist gets carried in the induction pipe to next cylinder, making it richer.

51. fuel flow spread should be less than 0.3 USG/H (first to peak versus last to peak) EGT spread unimportant highest versus lowest Lean test plotted out

52. fuel flow spread: (14,8 - 12,7) = 2,1 GPH : unlikely to be smooth LOP Lean test plotted out Moving the EGT probe a few mm deeper in the exhaust pipe will change the temperature maybe 100°F. Absolute EGT values are meaningless.

53. Is the effort required to run LOP worth it? Example 1: C421B with GTSIO-520 engines: ROP 32.5”/1800 rpm 42 GPH LOP 35” /1800 rpm 34 GPH producing exactly same power at 19% less fuel flow. In this case the power loss from running LOP is compensated by adding 2.5”MP. Example 2: On a normally aspirated Beech Bonanza, running LOP adds about one hour endurance, the savings in fuel cost alone pay for the engine overhaul at TBO time.

54. some quotes: “The aircraft owner, Bill, noticed the fuel flow down at 9.6 GPH and about had a cow. He thought something was wrong with his gauge because the EGT was reading right where he normally sees it (1410dF) and his CHTs were a bit cooler than normal which he attributed to the cooler air. He asked me what I thought was going on. I told him everything was just as it should be from my perspective and he said that couldn't be because the fuel flow should be reading 15 to 16 GPH.”

55. “I told him that I had seen his GAMIs and just assumed that he operated on the lean side of peak. He said that he did not and I asked if he would like me to return to the rich side and he said "Yes". I pushed in the mixture under his watchful eye and the EGTs went up and then came back down to 1410dF where we had started.... 50 degrees below peak, but on the rich side now. The fuel flow went from 9.6 to 15.5 and the CHTs went up from the 310 (average) to 360. Everything was back to where he normally operated.” thanks to Fred Scott, read full story at www.fwshome.com

56. some extra's

57. A lot of pilots reduce power after take-off and set 25”/2500 rpm. This is NOT a good idea, you are not doing your engine any favours.

63. Normal cycle for reference

64. “Light detonation” not too harmful, but may lead to higher CHT because of higher ICP which may lead to increasing levels of detonation if left unchecked.

65. “medium detonation” leads to increasing CHT needs to be checked, will probably damage the engine.

66. “heavy detonation” needs IMMEDIATE attention. will destroy your engine in seconds, not minutes.

67. chemistry (simplified) of combustion Stoïchiometric mixture: fuel = oxygen 'Peak EGT or leaner' 2 C 8 H 18 + 25 O 2 16 CO 2 + 18 H 2 O iso-octane fuel harmless carbondioxidewater vapour nitrogen left out of the equation since it doesn't change In pilot talk: “At Peak EGT or Lean of Peak”

68. chemistry (simplified) of combustion Rich mixture: fuel > oxygen C 8 H 18 + 12 O 2 7 CO 2 + 9 H 2 O + CO iso-octane fuel harmless carbondioxide water vapour nitrogen left out of the equation since it doesn't change carbon monoxide: poison In pilot talk: “Rich of Peak EGT”