Detonation Induced Engine Failure
Cylinders 3 and 5 are running higher than other cylinders as shown in the above display. The increased CHT's were within normal operating range. The GEM's data logging of engine performance clearly shows the CHT's normal pattern of operation.
The only symptoms are a slight drop in manifold pressure and a slight airframe vibration, that could easily go undetected. Only the GEM, clearly shows a sudden drop in cylinder 5 EGT, indicating possible cylinder failure.
The gradual loss of CHT in cylinder 5 as shown here by the GEM, verifies failure of that cylinder. All other cylinders continue to operate normally. Failure of cylinder 5 as clearly shown by the GEM, prompted the pilot to immediately shutdown the left engine.
The GEM display clearly shows that immediate shut-down secured the left engine to prevent further damage. Right engine continues to operate normally.
Post Flight Investigation
- After the incident, the customer contacted Insight for help. Based on Insight's analysis of the data log file, the hidden damage to cylinder 3 was revealed. The abnormal CHT's recorded in cylinder 3 and 5 forewarned of the detonation damage found in cylinder 3 and the failure of cylinder 5. These findings compared exactly to the easy to read picture the GEM displayed for it's owner.
- Left engine cylinder head 5 had separated from the cylinder barrel. Cylinder head 3 was found to be cracked. Had the pilot not shut down when he did, this cylinder would have failed too.
- The GEM's datalog analysis allowed the engine's real problem to be traced to its root cause. The fuel injection system was contaminated. The analysis also revealed hidden damage to cylinder 3. This cylinder would have certainly failed on a subsequent flight. Following these repairs the engine has been trouble free.
ENGINE FAILURE Case History
This case history is presented in the interests of economy and safety of flight. Analysis of the GEM datalog provides an excellent educational tool for understanding the complex relationships of engine management.
With the Advanced Graphic Engine Monitor (TM)ing with Data Logging provided by Insight's GEMINI, Daniel Knopper, an Aerostar Owner, was able to download critical in-flight engine behavior, as described and shown in this 3D graph, when his Aerostar Lycoming Engine failed due to detonation.
Daniel Knopper in his own words says;
"After landing safely, the stored data of Insight's Graphic Engine Monitor (TM) provided indisputable proof of proper operation to the overhaul facility for full warranty. Besides the unit showing the detonation of the failed cylinder, it revealed two additional cylinders encountering detonation range temperatures that normally would have gone undetected. Physical evidence was present on inspection of these cylinders and they were replaced by the rebuilder without any question.
Self diagnosis, trend monitoring and cost benefits don't compare to the restored peace of mind I have flying my Aerostar."
Discussion of Factors
Aircraft: Piper Aerostar 602P (Twin engine turbocharged pressurized high-performance six passenger)
Engine: Lycoming TIO-540-AA1A5 290 HP
Background: Maintenance Intensive aircraft.
A history of engine failures and in-flight engine shut-downs preceded installation of two new Engines and a GEMINI 1200 Graphic Engine Monitor (TM).
Abnormal combustion process:
Detonation and Pre-ignition are used to describe the same conditions within an engine. When diagnosing an engine failure, it is vital to know whether detonation or pre-ignition caused the engine failure.
Detonation and pre-ignition are totally separate conditions in terms of what they are and what damage they do. Detonation is caused by the spontaneous combustion of fuel in the combustion chamber verses a normal even desired burn. Detonation causes high cylinder head temperatures and low exhaust gas temperatures creating a pinging noise, that in aircraft engines you cannot hear.
Pre-ignition is premature ignition of the fuel/air mixture before the spark while the compression stroke is occurring, but earlier than desired. Pre-ignition can cause extremely high temperatures in a short time.
Causes of Abnormal combustion process:
Detonation can lead to pre-ignition if hot spots develop in the combustion chamber. Pre-ignition leads to detonation if combustion chamber temperatures raise the gas/air mixture to a high enough temperature to ignite spontaneously.
Detonation is caused by:
- · Too high a compression ratio for the octane of fuel used.
- · Too lean a fuel mixture, which slows the fuel burn and appears as an advance in timing.
- · Hot spots in the combustion chamber.
- · High power settings.
- · Pre-ignition
Pre-ignition is caused by:
- · Using an incorrect spark plug.
- · Hot spots in the combustion chamber.
Symptoms of Detonation/Pre-ignition:
CHT is usually increased, EGT may be decreased. Due to the wide variety of factors affecting CHT and EGT there is no simple or obvious way to detect abnormal combustion process!
Fuel Quality:
A fuels octane rating describes it's ability to resist detonation. Turbocharged engines require high octane fuel to offset the detonation inducing affects of high cylinder pressures and temperatures. Contamination of fuel by alcohol, jet-fuel or a lower grade of gasoline reduces it's octane-rating.
Injector Nozzles:
Restriction of fuel-flow by nozzle clogging increases back-pressure on the fuel system. This causes an increase in indicated fuel-pressure while fuel-flow is actually decreasing!
Pilot Technique:
Normal Aerostar Pilots Operating Handbook (P.O.H) recommended procedures were employed by the flight crew. Crew consisted of pilot/owner and maintenance chief. Both highly experienced on aircraft type.
Aircraft Status:
Fresh premium-rebuilt right engine. Low-time premium-rebuilt left engine. Newly-installed GEMINI 1200 system.
Prelude to Engine Failure
The aircraft departed a sea-level airport and performed a P.O.H. normal climb to 19,000 ft. Both engines appeared to operate normally in the climb. Level cruise flight was established at flight time 0.40. Cruise power was set and the right engine was leaned to P.O.H. recommended fuel-flow. All engine temperatures and pressures indicated well within normal operating ranges.
This datalog shows the subsequent events.
Daniel Knopper's own words
"During the first 100 hours after installing two premium rebuilt engines on my Aerostar, I encountered numerous problems including two in flight shutdowns. After the second engine change, I decided to install the Insight (GEMINI) Graphic Engine Monitor (TM).
During the first test flight, the left engine had problems to the extent of a third shutdown while climbing through 19,000 feet ASL.
After landing safely, the stored data of Insight's Graphic Engine Monitor (TM) provided indisputable proof of proper operation to the overhaul facility for full warranty. In addition to the unit showing the detonation of the failed cylinder, it revealed two additional cylinders encountering detonation range temperatures that normally would have gone undetected. Physical evidence was present on inspection of these cylinders and they were replaced by the rebuilder without any question.
After replacement of these cylinders, I determined that the #1 cylinder EGT peaked significantly sooner than the others with substantially higher fuel flow. After reporting this finding to my mechanic, he found the #1 fuel injector has a partial blockage, cleared it and everything now runs normally. This cleared up the problem encountered immediately after the first engine replacement, of much higher fuel flows on this engine than the other one at the same power settings. Nobody, including the engine rebuilder seemed able to explain the excess fuel flow with the higher EGT, until now.
Self diagnosis, trend monitoring and cost benefits don't compare to the restored peace of mind I have flying my Aerostar ".
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