Exhaust Emissions from In-Use General Aviation Aircraft (2016)

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Estimating Fuel Flows for Piston Engines 77 flows in this aircraft agree well with the exponentially modeled fuel flows, with the exception of the cruise engine state—The pilot executed a rich-cruise state which shows a fuel flow better aligned with the modeled flows. The cruise engine state is typically a leaned state, which differs from the mixture full-rich data used in creating the modeled fuel flows. In cases where no cockpit fuel flow is available, this method of estimating fuel flow produces numbers that agree with experienced pilots’ best guesses for fuel flow, even at idle and taxi. For Figure J-1. Plot of exponential equations used to estimate fuel flows for various engine types. 1.0 0.8 0.6 0.4 0.2 0.0 1.00.80.60.40.20.0 idle app rich cruiseT/O cruise taxi fr ac tio na l f ue l f lo w fractional engine RPM Lycoming O-360-A4M modeled fuel flow measured fuel flow Figure J-2. Measured fuel flow vs exponentially modeled fuel flow for a Lycoming O-360-A4M engine.

78 Exhaust Emissions from In-Use General Aviation Aircraft example, for the aircraft with a Lycoming O-320-E2G engine (Figure J-3), the pilot’s guess for fuel flow for all states is within 10% of the simulated value for all but the final approach engine state. This discrepancy is attributed to a bad guess on the part of the pilot. All of the above is taken into consideration in the protocol for assigning a fuel flow to a test point. Figure J-4 illustrates this protocol. Taxi App rich cruise T/O Final App cruise 1.0 0.8 0.6 0.4 0.2 0.0 fr ac tio na l f ue l f lo w 1.00.80.60.40.20.0 fractional engine RPM Lycoming O-320-E2G modeled fuel flow pilot guess Figure J-3. Pilot guess at fuel flow vs exponentially modeled fuel flow. Fuel Flow Gauge Exists? Fuel Flow Data for this State? Lean Cruise State? Use Measured Fuel Flow Use Modeled Fuel Flow Use Pilot Esmated Fuel Flow Start yes yesyes no no no Figure J-4. Flow chart for determining best fuel flow to use for a given test point.