PISTON ENGINES Part 3 Types of Piston Engine

Introduction Piston Engine Layouts Generally speaking, the more cylinders there are, the more power the engine will produce and the smoother the engine will run. The only limit to the variety of layouts is the designers imagination, except to say it is uneconomical (in manufacturing costs, capacity and use) to design and build a 4 litre V8 layout engine when a 2 litre V6 would do the job.

Introduction Piston Engine Layouts Single Inline 4 Inline 3 Inline 5 Vee 8 Vee 5 Vee Twin Vee 6

Introduction Piston Engine Layouts Horizontally Opposed (or flat) 4 Vee 8 Firing Order: - 1 – 4 – 3 – 2 1 – 8 – 4 – 3 – 6 – 5 – 7 – 2

The Two-Stroke Cycle As its name suggests, the operating cycle of this engine is completed in two strokes, down and up. i.e. one complete revolution of the crankshaft. Port A – Crankcase Inlet Port C – Exhaust Outlet Port B – Cylinder Inlet

Port A – Crankcase Inlet The Two-Stroke Cycle Piston pushed down forces fuel/air mixture into cylinder; Piston rising pulls fuel/air mixture into crankcase; (Induction) Stroke 1 Stroke 2 Compression is now causing combustion and out of the Exhaust valve Port A – Crankcase Inlet Port C – Exhaust Outlet Port B – Cylinder Inlet

Mechanical Arrangement The Petrol Engine The Diesel Engine This means that ignition is timed exactly when required without relying on the timing of a spark. Inlet Exhaust Same mechanical set-up as the petrol engine BUT without an ignition system or spark plugs

Mechanical Arrangement The Diesel Engine Combustion is initiated by the temperature increase in the compressed air/fuel mixture. Direct Injection Indirect Injection Inlet Exhaust Fuel is injected Indirectly into the inlet manifold, or Directly into the cylinder. Fuel needs to be injected to obtain the correct supply rate.

Mechanical Arrangement The Wankel Engine The piston rotates around the fixed pinion. This motion drives the rotating crankshaft. Which in turn drives the output shaft. Casing Rotating Triangular ‘Piston’ Fixed (non-rotating) Pinion Inlet Port Rotating ‘Crankshaft’ Output Shaft Exhaust Port Spark Plug The piston shape and the casing make the piston move up & down by a small amount as well. Points of contact

Mechanical Arrangement The Wankel Engine There are 3 chambers formed by the triangular rotor and the casing. As Chamber A rotates it draws in fuel/air (Induction) the chamber then gets smaller (Compression). Chamber B Chamber A The mixture is ignited by the spark plug in chamber B; (Combustion/Power) the expanding gases then force the rotor round. Inlet Port Exhaust Port As chamber C rotates, the exhaust port opens and the gases forced out. (Exhaust) Chamber C

Mechanical Arrangement Radial/Rotary Engines Radials and Rotary engines look similar; but in Radial engines, the crankcase and cylinders are stationary, and the crankshaft rotates the propeller. Whereas in Rotary engines, the crankshaft was stationary and the crankcase and cylinders rotated to drive the propeller. Crankcase Cylinders Propeller Mount Bolts Valve Gear Valve Pushrods Spark Plugs

Mechanical Arrangement Radial/Rotary Engines Radial Rotary Aircraft Nose (viewed from the front) (viewed from the side) Radial and Rotary engines were used commonly during WW2 in various transports, bombers and fighters. Rotary engines, whilst the best for power to weight ratio at the time, suffered some disadvantages - Gyroscopic effect – rotating such a large mass caused aircraft handling problems. Oil system – it was difficult to recirculate the oil, which literally splashed everywhere after leaving the engine.

Mechanical Arrangement Radial/Rotary Engines Radial Rotary Aircraft Nose (viewed from the front) (viewed from the side) But making an engine obsolete does not mean it disappears - Model aero engine 28 Cylinder Radial Engine Radial Powered Motorbike

Check of Understanding What is the limit to the variety of cylinder layouts? 12 cylinders 24 cylinders 36 cylinders No limit

Check of Understanding What is the operating cycle of a two-stroke engine? ¼ rotation of the crankshaft ½ rotation of the crankshaft 1 rotation of the crankshaft 2 rotations of the crankshaft

Check of Understanding What happens on the down stroke of a 2-stroke engine? Induction Compression Combustion/Power Exhaust

Check of Understanding Which of the following statements does not apply to a diesel engine? Same mechanical set-up as a petrol engine Ignition cannot be timed It has no spark plugs Fuel needs to be injected

Check of Understanding In a diesel engine, where is fuel directly injected? Into the piston head Into the inlet manifold Into the exhaust valve Into the cylinder

Check of Understanding In a Wankel engine, How many chambers are formed by the rotor and casing? Five One Seven Three

Check of Understanding In a Wankel engine, what happens in chamber A? Only Induction Only Compression Induction and Compression Exhaust

Check of Understanding Which of the following statements applies to a radial engine? The crankcase rotates The cylinders rotate The crankshaft rotates The crankshaft is stationary

PISTON ENGINES End of Presentation