L-Head Engine

The L-head engine, also called flathead, is an internal combustion piston engine whose valve configuration resembles the letter 'L' upside down. This type of four-stroke machine had both inlet and exhaust valves located on one side of the engine block. These are driven by push-rods actuated by one single camshaft, which allows the opening and closing of the valves at the proper time.

The L-head engine was commonly used in cars in the 1930s, 1940s, and early 1950s. They were very popular with hot rodders and racers. Today, it is employed in lawnmower, generators, and other industrial engines. Although L-head engines are less expensive to built, they produce more smog because of the high amount of surface area exposed to unburned fuel. They are also limited in their compression ratio and valve lift. Increased valve lift needs more clearance in the combustion chamber, which lowers compression.

Below, the photo shows an L-head Studebaker engine, with the cylinder head removed. You can see where the valves are situated in the block and how they are arranged.

A schemtaic drawing, showing the valve and rod configuration of an L-head engine.

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Cross Scavenged Engine

The cross scavenged engine is a two-stroke internal combustion machine which has a fairly simple port layout. In this type of engine, the scavenge flow normally arises from the crankcase and then flows to the transfer ports in a common duct. Both the scavenge ports and the exhaust ports are often drilled from the exhaust ports side in a single operation. Thus, it simplifies the manufacturing process.

The 'ears' of the deflector are usually centered about a diameter or are set slightly towards the scavenge side.The edge of the ears are usually chamfered at 45 degrees and given clearance from the bore so that they enter the combustion chamber above the tdc point without interference. In a cross scavenged engine, the deflection ratio of the cylinder and piston deflector in the design of the piston crown and the porting is 1.15.

The transition radius of the base of the reflector is not a particularly critical dimension as far as scavenging is concerned and it should be made approximately one third of the deflector height.

Below, schematic drawing of transfer port and deflector plan layout in a cross scavenged engine.

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Wright J65-W-18

The Wright J65-W-18 was an afterburning turbojet engine, which was used to power the Grumman F11F Tiger fighter aircraft. It could generate up to 7,450 lb of thrust and propel the aircraft to the maximum speed of Mach 1.2. It was a license-built version of the British Armstrong Siddeley Sapphire engine. Only 160 machines were produced between 1954 and 1958 in the United States.

The Wright J65-W-18 was an axial-flow type turbojet engine. It featured 13 compressor stages and 2 turbine stages, which rotated clockwise as viewed from the rear. The machine was equipped with an afterburner and a two-position convergent nozzle. An automatic control system for positioning the nozzle in afterburner mode was provided.

The Wright J65-W-18 had a four-element fuel pump, a self-contained lubricating system, and speed density type fuel control system. The rated thrust of the engine was as follows: a maximum thrust of 10,500 pounds; a military thrust of 7,450 pounds; and a normal thrust of 6,470 pounds. The fuel it burned was stored in a main and aft fuselage tanks.

Below, a photo of a cutaway Wright J65-W-18 on exhibition in a US Air Force museum.

A drawing of the F11F Tiger aircraft, showing the location of this turbojet engine in fuselage.

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Function of Turbine

The main function of turbine in an aero-engine is to drive the compressor. It also converts the energy from the hot gas flow coming from the combustion chamber into mechanical rotatory power that is imparted on the shaft; this is called torque. Additionally, the turbine must drive the accessories. In a turboprop engine, on the other hand, the primary function of turbine is to drive the propellers. In the case of a shaft engine, its main task is to drive the rotor blades of a helicopter.

Basically, turbine operation is not different from that of the compressor. While a compressor adds energy to the air flow passing through it by converting mechanical energy into pressure energy, a turbine conversely absorbs energy from the gas flow to convert it into mechanical shaft power or torque, which in turn drives the compressor. The great turbine power, which may reach values of 50,000 horsepower, is accomplished by extracting part, or sometimes all, of the energy contained in the hot gases, which are the product of combustion.

The amount of energy absorbs by the turbine is only as much as is required for driving the compressor and accessories (fuel pump, oil pump, electric generator). In aero-engines, the axial-type turbine is exclusively used because of the higher mass flow rate it makes possible. A radial-type turbine is, in fact, also possible. However, it is not a practical alternative. The design of the axial-type turbine can be single, or multi-stage.

Below, image shows the compressor, the shaft, and the turbine.

Simple schematic drawing showing the compressor, combustion chamber, the turbine and the shaft.

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Turbine Engine Stages

Aviation turbine engine stages are 1) air intake, 2) airflow pressure, which is done mechanically by the compressor, 3) fuel/air combustion, and 4) hot gas expansion, which is the conversion of hot gas into rotatory mechanical work, this being done by the turbine. This rotatory mechanical work is well harnessed at an AC power plant to drive a generator.

The reason why a jet engine is often referred to as a hot engine is because it uses hot gas to produce mechanical shaft power and thrust. Therefore, it transforms the chemical energy of the fuel combustion and the pressurized hot gas into rotatory mechanical power.

Generating thrust is possible only if the exhaust velocity of the gas is higher than the velocity at which air enters the engine through the intake. To accelerate the gas, energy must be added to the airflow within the engine, converting it into kinetic energy.

In a gas turbine engine, the increase of energy can be achieved in two consecutive steps and by two different adjacent engine components. First, pressure of the airflow is raised by the action of mechanical shaft power. This is done in the compressor portion. After it has been discharged from the high-pressure compressor, the pressurized air is heated in the combustion chamber, where gas temperature is steeply raised. The gas now is enough processed to provide mechanical work.

The first stage in the engine where hot gas in converted into mechanical power is the high-pressure turbine. As the hot gas expands and accelerates, it rotates the turbine with great force. After being discharged from the turbine, the gas is accelerated even further in the exhaust nozzle, where all remaining usable heat energy is converted into kinetic energy. The gas is ejected from the nozzle into the atmosphere where it will gradually dissipate to the conditions of the surrounding atmosphere.

Below, schematic drawing of an aviation turbine engine stages.

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Internal Combustion Engine Parts

The internal combustion engine parts are all the essential components that make up the machine that drives a vehicle. They are the cylinder, the piston, combustion chamber, connecting rod, crankshaft, valve, camshaft, block, carburetor, fuel injector, fuel, spark plug, exhaust, radiator. Each one of them plays an essential role, contributing to the overall purpose of the internal combustion engine, which is the conversion of the chemical energy contained in the fuel into a rotatory mechanical energy.

Cylinder- Each one of the circular cylinders contained in a block, in which the piston moves back and forth. 

Piston- The cylindrical-shaped mass which reciprocates back and forth in the cylinder, transmitting the gas pressure in the combustion chamber to the rotating chrankshaft. The top of the piston is called the “crown”, and the sides are called the “skirt”. 

Combustion Chamber- The end portion of the cylinder between the head and the face of piston. It is where combustion takes place. 

Connecting Rod- It is a rod connecting the piston with the crankshaft. 

Crankshaft- A rotating shaft, through which the engine work output is transmitted to external mechanical parts, such as differential gears and wheels. 

Valve- One of several round, flat-topped steel devices that regulates the flow of fuel into the cylinder at the proper time. 

Camshaft- Rotating shaft which pushes open the valves at a proper time in an engine cycle. 

Block- It is the body of the engine containing all the essential parts that make it work. It is usually made of cast iron, or aluminum. 

Carburetor- It is a flow device which regulates the proper amount of fuel, mixing it with air, into a combustible mixture. This process is called “carburetion”, which takes place in the cylinder. 

Fuel Injector- Pressurized nozzle which sprays the fuel into the incoming air on a spark ignition engine cylinder, or into the cylinder on a compression ignition engine. 

Fuel- It is the life and soul of the engine, setting in motion all its mechanical parts that propel the vehicle. It contains the chemical energy which is transformed into rotatory mechanical movement. It is done through explosion, which is a violent combustion. It could be gasoline, diesel, or natural gas, with the first two one being obtained from petroleum. 

Spark Plug- It provides gasoline engine cylinder with the spark that triggers the explosion, whose hot gases push the piston backwards. 

Intake Manifold- Piping system which delivers incoming air to the cylinders. 

Starter- A small electric motor geared to the engine flywheel that starts the engine. 

Exhaust- Flow system designed to remove exhaust residual gases from the cylinder away into the exterior. It is composed of an exhaust manifold, a thermal converter to reduce emission, a muffler, and a tail pipe. 

Oil- An important lubricant which reduces friction of the piston on the inside cylinder walls. It also contributes to cool down the engine, maintaining temperature at acceptable levels. Without oil, the engine would burn. 

Oil Pump- A device which carries oil from the oil sump to the required lubrication points. 

Radiator- It is a heat exchanger used to remove heat away from the engine coolant after the engine has been cooled. It is usually mounted in front of the engine.

Below, a cutaway drawing of a four-cylinder, 2.2 liter machine, showing the internal combustion engine parts, which make it work.

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Radial Engine

A radial engine is an internal combustion engine which has its pistons arranged in a circular pattern around a central crankshaft. The connecting rods of the pistons are connected to a master rod, which, in turn, is connected to the central crankshaft. A bank of cylinders on a radial engine is always composed of an odd number of cylinders, which ranges from 3 to 13 ones or more.

A radial engine operates in a four-stroke cycle, with every other cylinder firing and having a power stroke as the crankshaft turns around, giving the engine an smooth operation. Since it has four-stroke cycle, radial engine crankshaft requires two revolutions to complete the four strokes of each piston, which are intake, compression, combustion, and exhaust. Internal combustion radial engine has been used mostly on medium and large size propeller-driven aircraft. For large aircraft, two or three banks of cylinders are mounted together one behind the other on a single crankshaft.

The British Sopwith Camel biplane had the engine so mounted with the propeller fastened to the rotating bank of cylinders. One of the most famous radial engine used in aviation is the Continental R-670, which was made up of seven cylinders, displacing 668 cm³. However, it was the Yakovlev M-501 the biggest and most powerful radial engine ever designed. The gyroscopic forces generated by the large rotating engine mass allowed aircraft fitted with these engines perform astonishing maneuvers which was not possible with engines whose pistons were arranged in a line.

Below, an example of aviation radial engine; a Bristol Pegasus IIIM, 9-cylinder engine, which powered the Fairey Swordfish biplane.

Schematic drawing of a radial engine.

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