Engine Data Monitors Detonation and Pre-Ignition


Putting aside the debate about what is the most appropriate fuel mixture setting, and engine operation lean-of-peak, having a modern multi-channel engine monitor fitted enhances the safety of your aircraft.

By today’s standards a single channel EGT or CHT gauge is manifestly inadequate to indicate the current operating condition of air cooled piston aircraft engines. This is particularly so with higher horsepower and more complex general aviation piston engines.

Only a multi-channel engine monitor that has a CHT and EGT for each cylinder provides the pilot with sufficient information to show that the engine is operating correctly and safely.

Engine monitors with data logging allow the pilot and maintenance personnel to detect potential engine operating problems before they become safety issues. An engine monitor will identify problems such as:-

  • defective spark plugs.

  • partial blockage of a fuel injector nozzle.

  • cylinder cooling problems.

  • EGT’s can be used to check that the magneto timing is correct.

  • Using the change of each individual EGT when a magneto check is performed to confirm that the ignition system is working correctly.

  • detecting exhaust valve leakage and seating problems.

  • exhaust gas leaks. (e.g. cracked exhaust pipes)

  • providing hard data to maintenance personnel when there is an engine problem, and also confirming data that an engine problem has actually been fixed.

And importantly

  • detonation and pre-ignition which can cause catastrophic engines damage if not detected.

A simple defect such as a faulty spark plug can cause detonation which in turn can lead to pre-ignition even at “normal” mixture settings.

Without adequate instrumentation, a single spark plug costing $40.00 could be the critical linking factor that leads to the destruction of a $80,000.00 aircraft engine, or worse still, being the cause of a serious aircraft accident.

Consider for a moment, the normal variations that occur in manufacturing and in operation. In service, a spark plug typically experinces around 20 high temperature, and high pressure combustion events per second. Over time this can cause individual spark plugs to operate at a higher temperature than normal for a particular spark plug specification.

Given the right (or wrong depending on how you look at it) combination of circumstances such as high ambient temperatures, high cylinder head temperatures, and a mixture that is either not rich enough or not lean enough, in conjunction with this single spark plug that is operating hotter than its normal heat range could be the critical factor that causes pre-ignition in a cylinder.

While it is not possible for an engineer or pilot to identify the 1 in 10,000 1 in 20,000 spark plug that is operating outside of its specified temperature range by its appearance, a modern multi-channel engine monitor will rapidly detect the consequences of pre-ignition (very high cylinder head temperature and low exhaust gas temperature) and provide alarms to the pilot for corrective action to be taken (richen the mixture or reduce power if possible) to stop the pre-ignition event.)

If the pre-ignition is not identified, catastrophic damage can occur to the piston / cylinder / engine within 30 to 60 seconds.

A single cylinder CHT and EGT is clearly inadequate to reliably detect and avoid detonation and pre-ignition.

This one, of many, possible malfunctions scenarios, clearly highlights the safety benefit that modern engine monitors provide.