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A seminar and presentation report is submitted
in partial fulfillment of the requirements
for the final year (8th semester) award of the Degree
of Bachelor of Engineering in
GAJANAN C AVANTKAR
Under the Guidance of
DEPARTMENT OF MECHANICAL ENGINEERING
GOGTE INSTITUTE OF TECHNOLOGY
In today’s world it is possible to travel to any part of the world within short span of time
using air transport. Earlier aviation industry was not as well developed as today’; as they were
using Rotary Piston IC engines which limited the travel speed and distance; moreover the fuel
consumption of these engines was high leading to increased cost of transport.
A significant breakthrough in aviation industry took place with the advent of turbojet
engines which were Rotary -Reaction Turbine Engines which were much efficient than Rotary
piston engines and all other engines such as turbofan, turboprop, and turboshaft engines were
developed as improvement over turbojet engines.
This paper reviews the introduction to primary components of turbojet engines, principle
of operation, Newton’s third law of motion governing turbojet propulsion, Brayton cycle which
is governing thermodynamic cycle for open cycle gas turbines, vehicles currently employing
turbojet engines few advantages, disadvantages, applications & key differences.
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Internal combustion engines are "breathing" engines. That is to say, they draw in air and fuel for energy. This energy is realized as power when the air-fuel mixture is ignited. Afterward, the waste created by the combustion is expelled. All of this is typically accomplished in four strokes of the pistons. The greater emphasis on fuel economy, engine responsiveness, and emissions control has driven the ENGINEERS towards the development of turbochargers that serve distinct commercial diesel applications, along with reduction in NOx emmitions.
The basic principal behind turbocharging is fairly simple, but the real thing behind it is not as simple as it looks. A turbocharger is a very complex piece of machinery. Not only must the components within the turbocharger itself be precisely coordinated, but the turbocharger and the engine it services must also be exactly matched.
Development in automobiles has reached a systematic and logical extention. Specially automobiles today are recognized with their speed & optimum performance. To have only speed is easy but to have it with optimum performance is a difficult nut to crack.
You've heard the word "turbo" tossed around a lot, especially by performance car enthusiasts. But all you know is that it means an engine has more "oomph" to it than normal. But what exactly is going on underneath that hood? Let's open it up and take a look.
2. TURBO ENGINES:
The underlying basic truth about engine performance is that power output is directly tied to the total amount of fuel that can be burned in the engine. However, it takes air to support the combustion of fuel to create usable power, so increasing power begins with increasing airflow. There are many ways to increase total engine airflow, such as simply building a bigger engine. The real trick is to design an engine system that provides the desired engine airflow and power upon demand — without doing work necessary to pump that extra air into and out of the engine (and the fuel that must be mixed with it) when there’s not a demand for it. Ideally, this would be a small engine with huge power potential. Such an ideal design couples power with economy and efficiency — requirements that seem to be contradictory. Fortunately, such a design solution is both possible and practical. The answer to the above dilemma is turbo engines. A turbo can be a simpler, more compact way to add power, especially for an aftermarket accessory. A turbo can significantly boost an engine's horsepower without significantly increasing its weight, which is the huge benefit that makes turbo engines so popular!
For a given displacement you have to make power with RPM on a naturally aspirated engine. If you have a turbocharger, you make power with boost, and everything being equal, at lower RPM, with less friction and with better fuel economy."
The turbo engine unlike a naturally aspirated engine uses forced induction for its operation. Forced induction by pressurizing the intake of combustion ingredients increases the effective capacity of the engine without an increase in physical size. The forced induction approach has the advantage that the intake pressure may be regulated according to the engine speed, thus providing power from extra capacity at high speed, but without wasting fuel at lower speeds.
The advanced features a turbo engine has which naturally aspirated engines don’t :
• Charge air cooler.
A turbocharger is an exhaust gas driven supercharger. A turbocharger increases the power output of an engine while surviving extreme operating conditions. The typical boost provided by a turbocharger is 6 to 8 pounds per square inch (psi). Since normal atmospheric pressure is 14.7 psi at sea level, you can see that you are getting about 50 percent more air into the engine. Therefore, you would expect to get 50 percent more power. It's not perfectly efficient, so you might get a 30- to 40-percent improvement instead.
Turbochargers are a type of forced induction system. They compress the air flowing into the engine . The advantage of compressing the air is that it lets the engine squeeze more air into a cylinder, and more air means that more fuel can be added. Therefore, you get more power from each explosion in each cylinder. A turbocharged engine produces more power overall than the same engine without the charging. This can significantly improve the power-to-weight ratio for the engine.
In order to achieve this boost, the turbocharger uses the exhaust flow from the engine to spin a turbine, which in turn spins an air pump. The turbine in the turbocharger spins at speeds of up to 150,000 rotations per minute (rpm) -- that's about 30 times faster than most car engines can go. And since it is hooked up to the exhaust, the temperatures in the turbine are also very high.
Types of turbochargers:
VNT (Variable Nozzle Turbine Turbocharger)
Generates a higher air density at low engine speeds, allowing a greater input of fuel for the same air-fuel ratio, increasing power while making engines more fuel-efficient and cleaner burning. This technology improves low-speed driveability and high-speed fuel economy.
Multivane Variable Geometry Turbocharger with Rotary Electric Actuator
Employs a mobile multivane system composed of a number of vanes that pivot on their axis to modify the cross section. An electronically controlled rotary electric actuator helps to channel exhaust gas to the turbine wheel, enabling more precise control of boost pressure over the engine’s entire load and speed range. The result is improved torque, superior fuel economy and compatibility with on-board diagnostics systems.
VNT Slidevane models employ a mobile nozzle piston system to modify the cross section and offer Multivane™ variable technology in a simpler, more cost-effective package on applications in the 2.0- to 2.5-liter range.
An intercoolers primary function is to cool the charge of air after it has been heated due to boosting and the heat that is produced by turbo before sending the air into the engine .as the air is cooled, it becomes denser , and denser air makes for better combustion and more power.
In order to increase the power of the engine, the goal is to get more air molecules into the cylinder, not necessarily more air pressure. Additionally, the denser, cooler air helps increase the total amount of boost possible without causing engine knocking. Air to air intercoolers need to be mounted so as to maximize air flow and promote efficient cooling. Most cars such as the Saab (except the Subaru WRX based 9-2X Aero), Mitsubishi Lancer Evolution, Volkswagen and Audi use front mounted intercooler(s) (FMIC) mounted vertically near the front bumper, in line with the car's radiator.