Archive for October 2010
External Combustion Engine
An external combustion engine (EC engine) is a heat engine where an (internal) working fluid is heated by combustion of an external source, through the engine wall or a heat exchanger. The fluid then, by expanding and acting on the mechanism of the engine produces motion and usable work. The fluid is then cooled, compressed and reused (closed cycle), or (less commonly) dumped, and cool fluid pulled in (open cycle air engine).
"Combustion" refers to burning fuel with an oxidizer, to supply the heat. Engines of similar (or even identical) configuration and operation may use a supply of heat from other sources such as nuclear, solar, geothermal or exothermic reactions not involving combustion; but are not then strictly classed as external combustion engines, but as external thermal engines.
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| Diagram showing External Combustion Engine's Working |
"Combustion" refers to burning fuel with an oxidizer, to supply the heat. Engines of similar (or even identical) configuration and operation may use a supply of heat from other sources such as nuclear, solar, geothermal or exothermic reactions not involving combustion; but are not then strictly classed as external combustion engines, but as external thermal engines.
How Diesel Engine Work
One of the frequently asked questions to me from numerous people was "How diesel engine differs from a gasoline engine"
Both are internal combustion engine, both of them run on a 4-stroke cycle known as Otto-cycle, both convert chemical energy of fuel to mechanical energy by a series of small explosion in large number. So what's the basic difference, huh. The basic difference lies in the way fuel is induced in both the engine's cylinder. For better understanding of Diesel engine, do read our "How gasoline engine works" or 4-stroke engine works section and come back fast because now unfolding the biggest mystery of engineering that How Diesel Engine Work.
Technically, the difference between these engine lies in their Intake Stroke and Compression Stroke. In diesel only air is induced into the cylinder during Intake Stroke. Now piston moves up and compression stroke begins, this compresses the present air in the cylinder. The temperature of the air increases because on compressing or on reducing its volume the temperature of the air increases. Once the piston reaches the top or compresses the air fully, fuel is induced in the system. The temperature of the cylinder or system is high enough to ignite the fuel sprayed. An explosion occurs or Combustion Stroke begins this drives the piston back and after-that emission Stroke Occurs.
Diesel engine too have a 4-stroke cycle. These are:
Everyone has its pros and cons. Let's talk about the advantages and disadvantages of a diesel engine.
Pros
Both are internal combustion engine, both of them run on a 4-stroke cycle known as Otto-cycle, both convert chemical energy of fuel to mechanical energy by a series of small explosion in large number. So what's the basic difference, huh. The basic difference lies in the way fuel is induced in both the engine's cylinder. For better understanding of Diesel engine, do read our "How gasoline engine works" or 4-stroke engine works section and come back fast because now unfolding the biggest mystery of engineering that How Diesel Engine Work.
Technically, the difference between these engine lies in their Intake Stroke and Compression Stroke. In diesel only air is induced into the cylinder during Intake Stroke. Now piston moves up and compression stroke begins, this compresses the present air in the cylinder. The temperature of the air increases because on compressing or on reducing its volume the temperature of the air increases. Once the piston reaches the top or compresses the air fully, fuel is induced in the system. The temperature of the cylinder or system is high enough to ignite the fuel sprayed. An explosion occurs or Combustion Stroke begins this drives the piston back and after-that emission Stroke Occurs.
Diesel engine too have a 4-stroke cycle. These are:
- Intake stroke-Air is induced in the cylinder via intake port or pipe.
- Compression Stroke- Now the air present is compressed in order to increase the temperature of the air and also of the system.
- Combustion Stroke- Once the piston has completed the combustion stroke, fuel is introduced in which explodes due to high temperature of the system. This drives the piston back and hence combustion stroke comes into play.
- Emission Stroke-Now the piston comes back to remove the waste gases via exhaust port.
Everyone has its pros and cons. Let's talk about the advantages and disadvantages of a diesel engine.
Pros
- Highly fuel efficient engine. Have a greater mileage than that of gasoline engine
- Powerful boost. Diesel engine have less weight to compression ratio of cylinder and hence able to give much horsepower than a gasoline engine of its weight.
- Emit less CO2 and CO
- Produces sooty smoke, full of hydrocarbons leading to acid rain.
- It also generate nitrogenous compound which are very much harmful for the environment.
- These diesel engine has made their image like making clattering sound while moving. This is also posing a negative image on diesel engine while most of the gasoline engine don't produces much sound.
Secrets Behind NOS or Nitrous
When people talk about car race or racing games, the topic of NOS generally comes up. So actually what is NOS? How it Works?
Nos, Nitrous oxide (N2O) undergoes thermal decomposition and breaks up into Nitrogen and Oxygen, when heated at 300 degree C. Hence injection of NOS provides more oxygen during combustion. Technically, more oxygen in a cylinder means, more fuel can be induced in it leading to more power from that same engine. Hence a significant boost can be obtained from that same engine.
Moreover NOS also provides a cooling effect when it vaporizes. Specifically it absorbs the heat energy of the surroundings and vaporizes, leading to decline in temperature of intake pipe and the intake air. Hence due to less temperature of the air, volume of the air decreases and mass increases, or we can say that its density increases. Overall this all again leads to more availability of oxygen for combustion.
But there is only one major problem with Nitrous Oxide is that is very much bulky. A car needs a large amount of Nos, like any gas. Normally a 6 litre engine requires around 12,000 litre of air every minute running at 4,000 rpm, so it would need a tremendous amount of NOS to run a car continuously. So, a driver can only take a few minutes of NOS even after compressing it into liquid.
Moreover NOS also provides a cooling effect when it vaporizes. Specifically it absorbs the heat energy of the surroundings and vaporizes, leading to decline in temperature of intake pipe and the intake air. Hence due to less temperature of the air, volume of the air decreases and mass increases, or we can say that its density increases. Overall this all again leads to more availability of oxygen for combustion.
But there is only one major problem with Nitrous Oxide is that is very much bulky. A car needs a large amount of Nos, like any gas. Normally a 6 litre engine requires around 12,000 litre of air every minute running at 4,000 rpm, so it would need a tremendous amount of NOS to run a car continuously. So, a driver can only take a few minutes of NOS even after compressing it into liquid.
