Key points for low-temperature starting of aviation piston engines

When starting an aviation piston engine in a low-temperature environment, multiple key points need to be particularly noted to ensure that the engine can start smoothly and safely. The following are the detailed key points for low-temperature starting:

First, preparations and inspections before startup

Preheating

Where possible, store the aircraft in a heated hangar for preheating. If conditions do not permit, a portable heating furnace can be used to preheat the engine. Special attention should be paid to avoiding fire during the preheating process. Ensure that the heater is in good condition and do not leave the aircraft during the heating process. Keep the fire extinguisher in place.

Check the lubricating oil

Low temperatures can cause changes in the viscosity of engine lubricating oil, affecting the lubrication effect. Before starting, it is necessary to check whether the lubricating oil is sufficient and whether thermal insulation layers have been installed on the lubricating oil pipelines, various oil pressure sensor components, lubricating oil tanks, etc., to prevent the lubricating oil from freezing.

Battery maintenance

Low temperatures may cause battery power loss or ice formation inside the battery. Make sure the battery is fully charged or remove it and store it indoors.

Second, key points for startup operations

Start-up condition restrictions:

If the ambient temperature is at or below -40 degrees Celsius and the engine has been cold-immersed for 1 hour or more, do not attempt to start or cold forward the engine. Under the same conditions, if the machine is cold-immersed for 3 hours or more, it should not be activated or cold-forwarded.

Slow train operation

When the external temperature is below -35 degrees Celsius, before changing the position of the thrust handle, the engine should be allowed to run in IDLE for two minutes to allow the lubricating oil temperature to rise and ensure good lubrication of the engine.

Lubricating oil pressure monitoring

After startup, it may take a few minutes for the lubricating oil pressure to reach the normal working pressure. At this stage, the lubricating oil pressure may be higher than the normal range, and the bypass light of the lubricating oil filter may light up. The engine should be operated at a slow thrust until the lubricating oil pressure returns to the normal range. If the lubricating oil pressure remains higher than the normal range after the lubricating oil temperature stabilizes within the limit range, the engine should be shut down.

Warm-up of the display component

The display component may require more warm-up time to ensure that the engine indicator can accurately show the changes in values. During the warm-up process, the brightness of the display component may be lower than the normal display.

Third, Special starting methods (for specific engine types)

For certain types of aviation piston engines, special starting methods can be adopted to increase the success rate of low-temperature starting. For instance, an engine cold start method suitable for the complete decoupling of piston phase and valve opening and closing states includes:

Keep the intake valve open

At the initial stage of startup, keep the intake valves of the engine cylinders open. The starter drives the engine to accelerate from zero to the preset speed, allowing the rotating parts of the engine to store kinetic energy.

Periodically open and close the valves

After reaching the preset speed, the valves of the engine cylinder are periodically opened and closed. The stored kinetic energy and the torque provided by the starter motor are utilized to drive the engine to continue rotating until the engine speed reaches the ignition speed, the wall temperature of the engine cylinder reaches the preset cylinder temperature, and the gas temperature inside the cylinder reaches the preset gas temperature inside the cylinder.

Fourth, Precautions

Fire prevention preparations

When starting at low temperatures, excessive fuel injection is likely to occur. This excess fuel can wash the cylinder walls, which may cause scratches on the cylinder walls and lead to poor cylinder compression, resulting in hot starts. Excessive fuel injection can also cause an aircraft to catch fire. Therefore, fire prevention preparations should be made when starting up.

Prevent icing

In a low-temperature environment, the spark plug electrodes of an engine are prone to icing. If this happens, the engine will only run for a few cycles and then stop. The heat generated by combustion cannot continue to raise the temperature of the water produced by combustion, and the water will condense on the spark plug electrode and cause a short circuit. The only remedy at this point is heating.

Avoid excessive pressurization

After starting in a low-temperature environment, do not over-boost turbocharged or turbocharged engines. The appropriate intake pressure ratio or engine pressure ratio (EPR) should be determined using a power meter that is compatible with the pressure height and ambient temperature at that time.

In summary, the start-up of aviation piston engines in low-temperature environments requires a comprehensive consideration of multiple aspects such as preheating, lubricating oil inspection, and battery maintenance, and must be carried out strictly in accordance with the key points of start-up operation. For certain specific types of engines, special starting methods can also be adopted to increase the success rate of low-temperature starting.