Piston Engine Operations PISTON ENGINES Part 4 Piston Engine Operations (Oil and Fuel Pumps)

Introduction Oil Systems Lubrication is used between 2 sliding surfaces to overcoming friction, and therefore prevent or reduce component wear. The properties demanded from a lubricant vary considerably with the particular application. Lubricant for a bicycle is not suitable for a steam engine; a lubricating oil for any engine should be of a suitable viscosity for maximum loads and also retain this viscosity over the full range of engine temperature.

Oil Systems The ‘Wet Sump’ System Common to most vehicles Engine Block Pump Filter Common to most vehicles Oil is stored in the sump and pulled out, through a strainer, by a pump. The oil then passes through a filter to ensure it is clean etc. It then passes into the engine, returning excess oil to the sump. SUMP

Oil Systems The ‘Dry Sump’ System High Performance/Rally vehicles Engine Block Pump Filter High Performance/Rally vehicles and Aircraft Tank Oil is stored in a separate tank, but still pulled by pump through a strainer, and passed through a filter into the engine, returning excess oil to the sump. SUMP

Oil Systems The ‘Dry Sump’ System High Performance/Rally vehicles Engine Block Pump Filter High Performance/Rally vehicles and Aircraft Tank Scavenge Pump But the oil is then taken out of the sump by a scavenge pump & returned to the tank, hence the name ‘Dry Sump’ SUMP This gives protection against oil loss in cars; and helps maintain correct levels of lubrication in aircraft.

Oil Distribution Let’s take a closer look here. Oil flowing from the pump is passed through the filter, and then forced along internal passageways to the areas needing lubrication. The oil lubricates the ball and roller bearings, gear teeth, piston rings, cylinder walls and other moving parts, then drains to the sump. Let’s take a closer look here. Sump (Oil Tank) Pump Filter

Oil Distribution Bearing Lubrication A 4 CYLINDER ENGINE CRANKSHAFT The illustration shows the main bearing locations for: - Crankshaft support bearings. Conrod to crankshaft bearings (big-ends) for each piston. The gudgeon pins. In addition (not illustrated) are other bearings required to provide smooth running of other components such as the cam shaft, water pump drive shaft, oil pump drive shaft etc. Let’s take a closer look here. Flywheel Con Rod 1 2 3 4 Gudgeon Pin Front Support Bearing Rear Support Bearings Support Bearings Crankshaft A 4 CYLINDER ENGINE CRANKSHAFT

Oil Distribution Bearing Lubrication The illustration shows a cross sectional view of a plain bearing. The plain bearings are made up of two distinct halves, called ‘shell’ bearings, and the big-ends are fixed to prevent rotation in the conrod. Con Rod Big End Shell Bearings Crankshaft

Oil Distribution Bearing Lubrication The oil is fed into distribution grooves cut in the shells, spreading an even thin film of oil between the bearing and crankshaft surfaces. Excess oil is then returned to the sump. Oil Splash Con Rod Big End Shell Bearings Oil Distribution Groove Lubricating Oil Film Crankshaft Oil Splash Internal Oil Feed

Oil Distribution Bearing Lubrication Maintaining oil pressure is critical. In most cars a simple indicator light is illuminated. In performance cars and aircraft, a gauge is usual to display actual pressure. To prevent mechanical damage regular servicing is necessary. Oil specification is found in vehicle Owner Handbooks and Service Manuals, and aircraft Maintenance Manuals. Engine life in vehicles is monitored as miles travelled, while in aircraft it is as hours or cycles flown. Front Support Bearing Rear Support Bearings Support Bearings Gudgeon Pin Con Rod 1 2 3 4

Oil Pumps Internal Gear Type Pump This pump consists of two gears, one inside the other. The smaller centre gear is the driving gear, powered by the engine. The larger outer gear (‘idler’ gear) is driven by the inner gear via the meshing of the gear teeth or ‘lobes’. Pump Assembly (end plate removed) Pump Body Driving Gear Driven Gear Rotating Parts

Oil Pumps Internal Gear Type Pump The inlet and outlet ports are a known as kidney ports. Fluid is pulled in and forced out through these ports. As the gears rotate, fluid is pulled in and forced out. Pump Assembly (end plate removed) ‘Kidney’ Ports Pump Body Driving Gear Driven Gear Kidney Ports Yellow = Inlet Flow Red = Outlet Flow Rotating Parts

Fuel Pumps Where are the fuel tanks in most aircraft ? Aircraft fuel tanks are formed by the structure of the wing. Fuel can be transferred from tank to tank to help balance the aircraft in flight. This allows trimming the aircraft efficiently without using aerodynamic forces which cause drag.

Fuel Pumps The filler connection is usually underneath the wing and is a self sealing device to prevent spillage. It is also hidden away behind an access hatch to maintain aerodynamic smoothness. Fuel level is measured via a level sensor and indicated on the flight deck by the fuel gauge. The tank is filled from either a vehicle born bowser or underground storage tanks, as with vehicle filling stations. Filler Cap Cockpit Fuel Gauge Filler Neck E F 1/2 FUEL But to get the fuel to the engines, some form of pump is needed. Tank Fuel Level Sensor Fuel Pump Tank Cavity

Mechanical Diaphragm Pump One-way Inlet Valve One-way Outlet Valve Diaphragm Spring Driving Cam This is a Positive Displacement pump, which means when the pump stops, flow is prevented. This pump consists of a flexible diaphragm, which is moved up by spring force and down by an engine driven cam, and two one-way valves.

Solenoid Diaphragm Pump One-way Inlet Valve One-way Outlet Valve Diaphragm Magnetic Plate Solenoid Windings Switch Mechanism Another Positive Displacement pump. Consisting of a flexible diaphragm, moved up and down by an electro-magnetic force. In this pump, the piston is moved up and down by a magnetic field generated by the electrically powered coil underneath.

Fuel Pumps The Gear Type Pump The Gear Type Pump ‘SPUR’ GEARS BODY The Gear Type Pump is the most favoured pump design, because it consists of just a few easy to produce working parts. Intermeshing straight cut spur gears rotating in a close fitting body.

Fuel Pumps The Gear Type Pump As the gears rotate the fluid is carried ‘SPUR’ GEARS Flow Controller FLOW OUT As the gears rotate the fluid is carried between the gear teeth. A control valve is set to limit the absolute pressure in the system, (around 450 psi) to protect against system damage.

Fuel Pumps The Gear Type Pump Without the flow controller, Pump flow restriction in the controller causes pressure to increase ‘SPUR’ GEARS Flow Controller FLOW OUT Without the flow controller, the pump would provide a flow, but at no pressure. Pressure is only achieved because the flow control system works on flow restrictions which causes the pressure to rise.

Air Filter Fuel is pumped to the carburettor (which we will examine later). The carburettor controls the mixing of air and atomized fuel, but the air must be filtered to prevent any damage or blockage in the fuel system or engine. Air Filter Carburettor Inlet Exhaust We will look at this area Tank E F 1/2 FUEL Fuel Pump

Air Filter A paper based element bonded into a rubberized material, is concertinaed to get the greatest surface area. Air with contaminants passes through the filter, which catches the contaminants and leaves the air cleaner. Filtration rate is in Microns (1 micron = 0.000,001 metre). So a 30 micron filter stops particles of 30 microns or more. Air Filter Clean Air Filter of corrugated paper Dirt trapped by filter Air and Dirt

Check of Understanding Where would a Dry Sump Oil System be most commonly used? Most vehicles High Performance/Rally vehicles and Aircraft Only in Aircraft Only in High Performance/Rally vehicles

Check of Understanding What differentiates a Dry Sump system from a Wet Sump system? A Diaphragm Pump An Internal Gear Type Pump A Positive Displacement Pump A Scavenger Pump

Check of Understanding Bearings in a crankshaft are made up of two distinct parts. What are these called? Dry Bearings Roller Bearings Shell Bearings Ball Bearings

Check of Understanding Where would you find the oil specifications for an aircraft? The service manual The maintenance manual The operating manual The aircraft log

Check of Understanding Within an internal gear-type pump there are two gears. Which one is driven by the engine? The Idler Gear The Driving Gear The Outer Gear The Driven Gear

Check of Understanding Which of these pumps has a flexible diaphragm moved up and down by an electro-magnetic force? A Gear Type Pump A Mechanical Diaphragm Pump A Scavenger Pump A Solenoid Diaphragm Pump

Check of Understanding Which is the most favoured type of pump design? Solenoid Diaphragm Pump Gear Type Pump Mechanical Diaphragm Pump Meshing Gear Pump

Check of Understanding Without the flow controller in a gear-type pump, What flow would the pump supply? A flow at no pressure A flow at low pressure A flow at high pressure No flow at all

Check of Understanding What is a Micron? 1 1,000,000 of a metre of a metre 1 100,000 1 10,000 of a metre 1 1,000 of a metre

PISTON ENGINES End of Presentation