Gnome Rotary Engine

The Gnome was one of several rotary engines popular on fighter planes during World War I. In this type of engine, the crankshaft is mounted on the airplane, while the crankcase and cylinders rotate with the propeller.

The Gnome was unique in that the intake valves were located within the pistons. Otherwise, this engine used the familiar Otto four stroke cycle. At any given point, each of the cylinders is in a different phase of the cycle. In the following discussion, follow themaster cylinder with the green connecting rod.

Intake

During this portion of the stroke, a vacuum forms in the cylinder, forcing the intake valve open and drawing the fuel-air mixture in from the crankcase.

Compression

The mixture is compressed during this phase. The spark plug fires toward the end of the compression stroke, slightly before top dead center.

Power

 The power stroke happens here. Note that the exhaust valve opens early—well before bottom dead center.

Exhaust

This engine has a fairly long exhaust stroke. In order to improve power or efficiency, engine valve timing often varies from what one might expect.

When I first learned how these engines worked, I thought the only person crazier than the engine designer was the one who paid money for it. At first glance it seems ridiculously backwards.

Nonetheless, a number of engines were designed this way, including the Gnome, Gnome Monosoupape, LeRhone, Clerget, andBentley. It turns out there were some good reasons for the configuration:

• Balance

  Note that the crankcase and cylinders revolve in one circle, while the pistons revolve in another, offset circle. Relative to the engine mounting point, there are no reciprocating parts. This means there's no need for a heavy counterbalance.

• Air Cooling

  Keeping an engine cool was an ongoing challenge for early engine designers. Many resorted to heavy water cooling systems. Air cooling is quite adequate on rotary engines, since the cylinders are always in motion.

• No flywheel

  The crankcase and cylinders provided more than adequate momentum to smooth out the power pulses, eliminating the need for a heavy flywheel.

All these factors gave rotary engines the best power-to-weight ratio of any configuration at the time, making them ideal for use in fighter planes. Of course, there were disadvantages as well:

• Gyroscopic effect

  A heavy spinning object resists efforts to disturb its orientation (a toy gyroscope demonstrates the effect nicely). This made the aircraft difficult to maneuver.

• Total Loss Oil system

  Centrifugal force throws lubricating oil out after its first trip through the engine. It was usually castor oil that could be readily combined with the fuel. The aircraft's range was thus limited by the amount of oil it could carry as well as fuel. Most conventional engines continuously re-circulate a relatively small supply of oil.

Most of my information on the Gnome came out of Air board Technical Notes⁷

Wankel Engine

The Wankel rotary engine is a fascinating beast that features a very clever rearrangement of the four elements of the Otto cycle. It was developed by Felix Wankel in the 1950s.In the Wankel, a triangular rotor incorporating a central ring gear is driven around a fixed pinion within an oblong chamber.

Intake

The fuel/air mixture is drawn in the intake port during this phase of the rotation.

Compression

The mixture is compressed here.

Power

The mixture burns here, driving the rotor around.

Exhaust

And the exhaust is expelled here.

The rotary motion is transferred to the drive shaft by an eccentric wheel (illustrated in blue) that rides in a matching bearing in the rotor. The drive shaft rotates once during every power stroke instead of twice as in the Otto cycle.

The Wankel promised higher power output with fewer moving parts than the Otto cycle engine; however, technical difficulties interfered with widespread adoption. In spite of valiant efforts by Mazda, the four stroke engine remains much more popular.

Audi-A8

Audi has launched it’s all-new A8 L executive saloon in India with a starting price tag of Rs 87.32lakh (ex-showroom, Mumbai). The new A8 will take on the competition to the likes its other German rivals namely BMW 7-series and Mercedes S Class.

Offered only in an extended wheelbase model, the new A8 L will maximize what Audi does best: lots of high-quality engineering, plus artful design inside and out.

"The introduction of Audi A8 L is a landmark achievement for Audi India as it celebrates our past successes and foreshadows future growth," Audi India Head, Michael Perschke said.

The new A8 L offers both luxurious ride comfort and sporty handling. It is once again, based on a virtually all-aluminum body/chassis structure, which combines high strength with relatively light weight (for its size).

The A8 Long Wheelbase is five inches longer between the axles and overall length than the standard-wheelbase A8 which will not be available in India. Most of that extra dimension shows up in the rear-passenger compartment; there's an option group that includes reclining rear seats, massage, and foot rests.

On the inside there’s an all-new interior. The gear selector is now an electronic shifter, with four positions; Audi says it’s shaped like the thrust lever on a powerboat. The MMI system has been moved from the centre console to the fascia, and now features a touchpad panel, which allows you to write letters or numbers on the screen to enter phone numbers or navigation destinations.

At present, the A8 L will only be available with a 4.2-litre FSi motor, followed by the 3.0-litre TDi in March. Going forward, the German giant will launch the 500bhp 6.0-litre W12 petrol variant during Diwali this year. The 4.2-litre V8 TDI variant – the same engine that made the A8 a popular choice in the foreign markets – will also make its way to India by early 2012.

Four Stroke Engine

The four stroke engine was first demonstrated by Nikolaus Otto in 1876, hence it is also known as the Otto cycle. The technically correct term is actually four stroke cycle. The four stroke engine is probably the most common engine type nowadays. It powers almost all cars and trucks.The four strokes of the cycle are intake, compression, power, and exhaust. Each corresponds to one full stroke of the piston; therefore, the complete cycle requires two revolutions of the crankshaft to complete.

Intake

During the intake stroke, the piston moves downward, drawing a fresh charge of vaporized fuel/air mixture. The illustrated engine features a poppet intake valve which is drawn open by the vacuum produced by the intake stroke. Some early engines worked this way; however, most modern engines incorporate an extra cam/lifter arrangement as seen on the exhaust valve. The exhaust valve is held shut by a spring (not illustrated here).

Compression

As the piston rises, the poppet valve is forced shut by the increased cylinder pressure. Flywheel momentum drives the piston upward, compressing the fuel/air mixture.

Power

At the top of the compression stroke, the spark plug fires, igniting the compressed fuel. As the fuel burns it expands, driving the piston downward.

Exhaust

At the bottom of the power stroke, the exhaust valve is opened by the cam/lifter mechanism. The upward stroke of the piston drives the exhausted fuel out of the cylinder.

What is Mechanical Engineering?

Mechanical engineering, as the name implies, deals with the mechanics of operation of mechanical systems. The various functions that fall within the scope of this branch of engineering are designing, manufacturing and maintenance of mechanical systems. For this purpose it uses the various laws of physics and applies them to different systems to analyze their performance and map out ways to improve their efficiency.

History of Mechanical Engineering

Mechanical engineering experienced its growth during the time of the World Wars. This growth can be attributed to the need for building newer war machines during that time. As a result of this need, more money was allocated towards research in this field and hence it began to develop as a unique area of study. Over the years, mechanical engineering has expanded its scope and it now has a noteworthy role to play in all other areas of engineering also.

Applications of Mechanical Engineering

Mechanical engineers are involved in the design and construction of various pieces of equipment like aircrafts, spacecrafts, and automobiles, stationary structures like building and bridges and industrial machinery. Due to the fact that mechanical engineers have to deal with a wide range of issues relating to different fields during the course of their work, the mechanical engineering program is prepared to provide them with the basic knowledge of different areas of study.

Just as chemical engineers strive to make different chemical processes cost-effective, mechanical engineers also strive to make the production and maintenance of different machines economical and efficient. Mechanical engineers also have to deal with one additional issue. The machines designed and manufactured by these mechanical engineers will be used by general community who do not have any knowledge about their operation. Hence, they will have to consider the safety and durability factors of these machines also while designing them.

Areas of Study Of Mechanical Engineering

The main areas of study that mechanical engineering looks into are:

• Design
  • Drafting and analysis – For this purpose it uses design softwares like Pro-E, Catia, Ansys and AutoCAD.
  • Design of various mechanisms – In this purpose, the kinematics and dynamics of a mechanism are taken into account and a proper design is drafted for the mechanism.

• Manufacture
  • Solid Mechanics
  • Strength of Materials

• Statics and Dynamics
• Heat-related Studies
  • Thermodynamics
  • Heat Transfer
  • Energy Conversion
  • Refrigeration and Air Conditioning
• Fluid Mechanics, Hydraulics and Pneumatics
• Instrumentation and Measurement

Mechanical engineering is finding more and more applications these days in other areas of engineering also. The most significant of these is the field of robotics. Robotics has become an important area of study due to the fact that more and more processes are getting automated these days. Mechanical engineers are handed the task of manufacturing assembly lines of robots for different operations and controlling them through pre-written programs to make the process of manufacture less human dependant, and more efficient and economical.