Akroyd Engine

Akroyd Engine Lab Report

How does it work?

The Akroyd Engine uses the Otto cycle, hence consist of induction, compression, expansion and exhaustion. Starting with the piston at top dead centre (TDC), the piston moves downwards and increased the volume inside the cylinder in the process reducing the pressure. This occurs while the inlet valve is open hence a mixture of air and vaporised fuel from the hot-bulb, is drawn into the cylinder. As the piston comes to bottom dead centre (BDC) the valve closed and the piston moves back up the cylinder compressing the air/fuel mixture inside of it. As the piston approaches TDC, this compressing caused the temperature of the mixture to rise to a point where the fuel will ignite. This ignition causes and releases energy from the fuel to the gases inside of the cylinder, causing pressure forces on piston, pushing it back down the cylinder. This is the expansion stroke and this is where work is actually done on the piston, (in all other strokes work is done by the piston). As the piston now comes to BDC and the exhaust valve opens and allows the exhaust gasses to be pushed out of the cylinder as the piston moves up cylinder again, allowing for another induction stroke to follow.

The piston is connected to the connecting rod which connects the piston to the crankshaft. As the piston is pushed down during the expansion stroke, the crankshaft will receive the energy and turn, and during the other strokes the crank will drive the piston up the cylinder. This is of course is actually done by the flywheel. The flywheel is a large and heavy so when it is spinning it contains a lot of inertia which keeps the engine going through the non-power strokes.

The valves

The crankshaft is connected to the camshaft and geared so that it rotates with half the angular velocity on the crank (since each valve opens once every cycle, or two revolutions). The purpose of the camshaft is to open and close the valves via the lobe at the end of the camshaft pushing against the valve lifter and causing the rocker arm to open the valve. In order to aid in better induction and exhaustion of gasses valves do not open and close exactly on dead centre. An inlet valve will open slightly before TDC and close slightly after BDC, whereas an exhaust valve will open slightly before BDC and close after TDC. The reason for this is so that the valve is well open though the relevant stroke allowing for clearer passes for gasses, since it takes a bit of time for valves to open or close fully.

The Governor

The governor regulates the speed of the engine by regulating the flow of fuel to the engine. The governor in this case works by two balls spinning around relative to the speed of the engine. As the engine speed increases the centrifugal forces on the balls becomes greater and they move outwards. In moving outwards the governor mechanism is designed so that a needle valve opens causing some of the fuel to bypass the injector and return to the fuel tank. As there is now less fuel per stoke in the cylinder there is less work done by the engine and