As of today aviation fuel costs are down but that in itself is no reason to fly Rich of Peak (RoP) unless you really need to. Flying Lean of Peak (LoP) not only saves money on your fuel bill, it also keeps your engine cleaner which means you would be saving on maintenance costs as well.
But to know whether or not you are saving anything, you need modern sensors connected to modern digital gauges installed in your cockpit. These modern digital gauges should include a Exhaust Gas Temperature (EGT) gauge, a Cylinder Head Temperature (CHT) gauge and a highly accurate Fuel flow indicator like the digital fuel flow indicator manufactured by JP Instruments.
When you run the aircraft engine using the RoP technique, there is an excess of fuel in the cylinder. While this may help keep the engines cooler, the exhaust ends up contaminating the oil and creating a hell of an overall mess including quicker carbonisation. There simply is no reason to be running the aircraft in the RoP technique. Also, cylinder pressure is much higher (between 80 to 100 psi) in RoP than in LoP.
Let us understand how you save money with LoP. When you operate the cylinder in LoP, it results in a longer, gentler, slower push on the piston because the peak cylinder pressure develops later from piston top dead centre than if the cylinder were to be operating in RoP. This means the EGT Gauge pressure only develops when the piston has travelled further along its downward stroke. So instead of a hammer blow (as in the case of RoP), there is now a gentle push because the piston inside the cylinder has already travelled far into the downward stroke of the cycle.
Higher cylinder pressure equates to higher CHT's. So in reality, operating RoP will result in higher internal cylinder pressures which in turn results in higher CHTs. whereas operating LoP at exactly the same Horse Power as the cylinder operating RoP will result in roughly 35°F lower CHT's. So your aircraft engine can actually run LoP at a lower CHT while producing the same horse power i.e. better speed, lesser fuel flow (as confirmed by the digital Digital EGT Gauge), lower Cylinder Head Temperatures – isn't that what every pilot wants?
Besides, when the aircraft engine is running in LoP, all fuel in the cylinder is used so there is nothing to blow back and contaminate the oil. Lower CHT and cylinder pressure also means lesser carbon deposits settling on the internal engine components as well so you save on the maintenance bill too.
A common misconception amongst most pilots is that you only operate LoP at low power settings. In reality, you can operate at up to 75% power without using a lot more fuel and this will be proved by your digital fuel flow indicator.
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