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Old 14th May 2015, 18:20   #1
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Default Explained! The different types of Petrol Engines (Inline, Flat, V etc.)

Felt that sliver of frustration when automotive programs talk about a delicious type of engine on a new car they're reviewing, and you wished you could connect better with the characteristics of that engine the presenters were talking about?! Here's a potential reduction to that frustration, alongwith using cool techno-lingo with your friends to increase their awe at your technical expertise !

This thread attempts to capture the categories of petrol/gasoline engines currently in vogue across international automotive markets. This should also serve towards a historic perspective of these engines, and their typical applications.

This is a compilation from various expert technical articles across the internet, alongwith my own understanding. Credit to the salient sources are at the bottom of this thread.

Broadly, there are currently 5 types of configurations of petrol/gasoline engines that I care to categorize them into. Read on.


1. Straight/Inline engine

This is the most popular and widely used engine configuration today. Almost all the mainstream production cars that you are aware of use this engine configuration.

Configuration:
  • Cylinders are arranged next to each other - in a straight line
  • Cylinders sit on top of the crankshaft
  • Simple construction: a single cylinder head, cylinder bank and valve train
  • Contains relatively lesser moving parts than the other engine configurations
  • Typically a single exhaust manifold
Two of the best examples of inline engines are:

Inline-Four: The junta engine really! 4 cylinders in a straight line. Its there in all mainstream cars you know, including your Maruti. Although there are fewer cylinders offered today, the inline-four is genesis.

A DOHC inline-four:
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Straight-Six: The Straight-six is a European favorite - ask BMW and Audi. Think of it as an inline-four with 2 additional cylinders bolted on, to make it a 6-cylinder affair.
Why do BMW/Audi love the Straight-six? Its one of the most refined engines out there, with its firing order making it an extremely well-balanced engine.

A much-loved BMW straight-six that powered an earlier Z4 drop-top sports car:
Explained! The different types of Petrol Engines (Inline, Flat, V etc.)-straight-six.jpg


Advantages:
  • They are compact/light and therefore lend themselves to better fuel efficiency. The same reason makes them ideal for front-wheel drive cars (which is most of the mainstream productions cars)
  • More economical to manufacture and maintain.
  • Here's a reason that all BHPians can immediately relate to: inline-fours respond well to tuning!
Disadvantages:
  • Certain imbalances tend to limit the maximum size that an inline-four engine can attain. Typically, not more than 2.5/3L.
  • Higher center-of-gravity (CG) compared to some other engine configurations.
  • They tend to lack the rigidity of the Flat/Boxer and V-type engines, due to their longish layout - especially the straight-six engine.


2. Flat/Boxer engine

We now move into the realm of performance engines! Although the number of manufacturers that use the boxer engine have dwindled, with Porsche and Subaru continuing to persist with the boxer engine in their current offerings, the automotive/racing world has fond memories of this engine layout.

This engine configuration was made famous by the original VW Beetle, which used an air-cooled, rear-mounted boxer engine.

Configuration:
  • The biggest design departure with an inline engine is that a boxer engine has horizontally opposed pistons.
  • These horizontally opposed pistons are contained in 2 cylinder banks, on either side of a common crankshaft.
  • Due to this layout, boxer engines are very low and also wide.
A video of a Subaru boxer engine in action (I love such videos!):

Advantages:
  • Well-suited for motor-racing, due to its low CG which translates to better handling
  • One of the smoothest engines, due to excellent inherent balance. In fact, this engine, alongwith the Straight-Six and V-type engines, forms a rarified group of the best balanced engines of all time.
  • Due to this excellent balance, there is lesser weight on the crankshaft. This translates to a reduced power loss.
Disadvantages:
  • Its a wide engine. Maintenance can get tricky if its housed in a tight engine bay.
  • Tends to be a bit more raucous than an Inline engine.
  • They are more complex - with two cylinder heads/valve trains.
While on the topic of Flat/Boxer engines, notable mention must be made of a rare flat engine - the Flat-12 engine. Although strictly not a boxer engine, it can be categorized as a flat engine primarily because it was a 180-degree V-engine. The pedigree of the Flat-12 is summarized below:
  • Ferrari perfected a Flat-12 and used it in the Testarossa and Berlinetta Boxer
  • This also inspired Alfa Romeo, who used it in some of their endurance racing cars
  • Mercedes-Benz used a clever flat-12 in their C291 endurance racing car
  • Porsche developed an air-cooled flat-12 to be used in their 917 endurance racing car. These 917s proved so dominant over the competing Ferraris of the time that it forced Ferrari to invest in a flat-12 design of their own.

Last edited by theMAG : 23rd May 2015 at 01:59. Reason: Edited
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Old 15th May 2015, 20:23   #2
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Default re: Explained! The different types of Petrol Engines (Inline, Flat, V etc.)

3. V-engine

We now enter a much vaunted performance temple that most have heard of. We've all had atleast one wall poster or a desktop wallpaper of a fire-breathing V12 car, that is the equivalent of automotive pornography!

These engines derive their name from the V-shape that their cylinder banks are in, on either side of the crankshaft.

Configuration:
  • Cylinders are located in a V-angle, on either side of a common crankshaft
  • The angle of the V varies between manufacturers, although ones where the V angle is 90 degrees is preferred in some racing applications.
  • Denoted by the numbers of cylinders, a V-configuration engine is a V6, V8, V10 or V12. The V2- used in motorcycles, is called a V-Twin.
  • Note that the V16 engine is no longer used in automotive applications, since its smaller siblings - the V10 and V12 provide similar output characteristics, at far lower costs
  • Higher the number of cylinders, closer does that car get to being a supercar- with the V12 engined cars occupying the highest pecking order in a car's society!
  • 2 exhaust manifolds

The V12 of the iconic McLaren F1 supercar:
Name:  Mclaren V12.jpg
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Advantages:
  • Dimensions are compact - which are appreciated either in construction of road cars or race cars
  • The compact dimensions mean that more cylinders can be packed in, as comparable to an inline/straight engine of similar dimensions.
  • Can accommodate higher displacement cylinders, and therefore that extra power
  • Its a strong engine - which makes it ideal for racing applications
  • Can accommodate higher compression
  • High levels of refinement.

Disadvantages:
  • Contains more moving parts, resulting in higher cost/complexity
  • Weight. The same technicality above makes a V-engine heavy.
  • Due to environmental concerns, the naturally aspirated V12 engine might be in its swan song. Supercar manufacturers have started adapting to turbocharged/supercharged (in some cases, both!) V6 engines with lesser displacement and clever engine management systems.

This writeup can never be considered complete without mention of the greatest V-engined cars in history! Notable mentions below:
  • McLaren F1: the Gordon Murray designed template that introduced modern world to hitherto-unseen engineering and performance seen in a road-going supercar. It came with a BMW-developed naturally aspirated V12.
  • Lamborghini Countach: the "welcome to the future" Marcello Gandini-designed wallpaper car that has adorned the walls of millions of people worldwide while growing up! The Countach was powered by Lamborghini's 4 liter V12 initially, before evolving into a 5 liter V12 by the end of its production run.
  • The fastest Chevy Camaro muscle car ever made: the 2012 Camaro ZL1, came with a 6.2 liter supercharged V8
  • Honda NSX: created disruptive change in the automotive world, and came with a 3 Liter V6 that knew no upper rev limits (literally)!


4. Rotary/Wankel engine

If ever there was a giant-killer in the engine world, its the Wankel engine. A very clever engine design that produced power comparable to engines much larger in size, with fewer moving parts, it finds mention here for what it represented, although its no longer in production today.

Mazda became synonymous with the Wankel engine, persisting and improving its design, till the last Wankel-engined Mazda in 2012, when the Wankel engine met its demise due to pollution norms.

Configuration:
  • No pistons! Used rotors instead.
  • Crankshaft remained stationary - the whole cylinder block moved around it instead
  • A 3-sided symmetrical central rotor placed around an eccentric shaft, in an oblong housing
  • A single rotation of the rotor covered all 4 strokes- intake, compression, ignition and exhaust.

An animation of a Wankel engine at work:


Advantages:
  • High power-to-weight ratio: as powerful as engines much larger than it
  • Compact dimensions, due to few moving parts
  • Economical to manufacture, for the same reason
  • Simple yet effectively engineered
  • High revving
  • Refined

Disadvantages:
  • It was a thirsty engine, with higher emissions than conventional piston engines
  • Its biggest Achilles Heel by far, was compression problems primarily due to the rotary seals giving way, being unable to cope with the temperature differences along its periphery. This often required engine rebuilds.
Ironically, the only Japanese manufacturer to ever have won Le Mans was - you guessed it, Mazda, with their Wankel-engined 787B endurance racer, which really highlighted the potential of this engine. Other Wankel-engines cars worthy of mention were, not surprisingly, the Mazda RX7 and RX8 sportscars.


5. W-engine

This is an extremely un-common engine configuration, with VW currently the only manufacturer of the W-type engine - the W16. This is a rather famous engine, used in the world-record shattering Bugatti Veyron hypercar, with 10 radiators, not less!

VW also recently announced a new W12 engine with its group company Bentley.

Configuration:
  • Cylinders are arranged in the shape of a W (or 2 tight Vs)
  • 4 cylinder banks sharing a single crankshaft
  • 2 cylinder heads, 2 camshafts

The Bugatti Veyron W16 engine:
Explained! The different types of Petrol Engines (Inline, Flat, V etc.)-volkswagen_w16.jpg

Advantages:
  • The major advantage is the relatively compact engine footprint- for an engine with an enormous number of cylinders.

Disadvantages:
  • Higher operating temperatures
  • Complexity
  • Cost

The most famous car with a W engine has been mentioned earlier- the Bugati Veyron, with a W16 engine, and boosted to attain 1001 hp. The other cars to have used a W-engine, all from the VW Group, were the Passat (W8), while the Phaeton, Touareg, Audi A8 and Bentley Continental GT all used a W12.

This wraps up this overview of petrol/gasoline engine configurations. I hope you enjoy reading it as much as I enjoyed putting it together.


CREDITS

http://cosmone.com/auto/discover/types-car-engines
http://www.carthrottle.com/post/engi...-engine-types/
http://www.rapid-racer.com/car-engines.php
http://vwvortex.com
http://en.wikipedia.org/wiki/Wankel_engine
http://en.wikipedia.org/wiki/W_engine
Wikipedia (for searches that I dont remember now).
All photos/videos copyright their respective owners.

Last edited by theMAG : 16th May 2015 at 22:40.
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Old 16th May 2015, 22:50   #3
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Default re: Explained! The different types of Petrol Engines (Inline, Flat, V etc.)

Moved from Assembly Line to Technical Stuff !
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Old 17th May 2015, 14:23   #4
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Default re: Explained! The different types of Petrol Engines (Inline, Flat, V etc.)

Quote:
Originally Posted by theMAG View Post
Felt that sliver of frustration when automotive programs talk about a delicious type of engine on a new car they're reviewing, and you wished you could connect better with the characteristics of that engine the presenters were talking about?! Here's a potential reduction to that frustration, alongwith using cool techno-lingo with your friends to increase their awe at your technical expertise !
Nice and informative thread.

Another configuration is Radial piston type. It was used widely in the aircrafts, once upon a time.

http://www.mekanizmalar.com/radial_engine.html
http://photovalet.com/MYOV01P10_08.html
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Old 18th May 2015, 11:22   #5
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Default Re: Explained! The different types of Petrol Engines (Inline, Flat, V etc.)

You missed the W18 engine. It had three banks of six cylinders each.
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Old 18th May 2015, 14:48   #6
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Default Re: Explained! The different types of Petrol Engines (Inline, Flat, V etc.)

Thanks @theMAG for an informative write-up. Made a good read on one of my favorite topics.
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Old 18th May 2015, 18:28   #7
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Default Re: Explained! The different types of Petrol Engines (Inline, Flat, V etc.)

Great info. Thanks a lot.
I had always wondered how the wankel shaft engine worked. That video explains it quite well.
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Old 18th May 2015, 18:38   #8
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Default Re: Explained! The different types of Petrol Engines (Inline, Flat, V etc.)

For academic purposes, maybe we can add one more type to the list.
Axial piston Engines.

Duke - http://www.dukeengines.com/

The Duke engine is a four stroke "axial" reciprocating engine. "Axial" because the axis of each cylinder is aligned with the axis of the output/crank shaft. Axial engines are sometimes called 'barrel' and 'Z-crank' engines. The former refers to the cylindrical shape of the Cylinder Group whilst the latter alludes to the shape of the Crankshaft. The 'Z' in the crank provides the journal surfaces upon which the combustion loads (via conrods and then a swashplate, or the case of the Duke engine a 'Reciprocator') act to provide the driving torque of the engine. The uniqueness of the Duke Engine is the combining of these two motions in a counter-rotating configuration which results in a myriad of mechanical and performance advantages.
So far the prototype and developmental engines have run on petrol of various octane levels (91 through 98 octane) and kerosene based Jetfuel without modification.
Duke's challenges in seal development are much less than in a 2-stroke or in the Wankel engine due to lower sliding velocity and a flat monoplane sealing surface (Wankel has 3 seal faces, 1 curved, that meet at a corner, seals).
Axial engines are challenging to make practicable at typical engine operating speeds.
Attached Thumbnails
Explained! The different types of Petrol Engines (Inline, Flat, V etc.)-duke.jpg  


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Old 18th May 2015, 19:23   #9
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Default Re: Explained! The different types of Petrol Engines (Inline, Flat, V etc.)

Quote:
Originally Posted by jfxavier View Post
For academic purposes, maybe we can add one more type to the list.
Axial piston Engines.
Useful information jfxavier.

The axial piston machine is already used for hydraulic motors (the motors that run on pressurised oil flow). In reverse way, it is also used for pumps; the shaft is rotated by motor and the machine pumps oil.

So, the engine based on this mechanism is a good idea. Only challenge compared to hydro-motor is high temperature and high momentary combustion loads. This will demand better metallurgy.

For smaller sizes upto around 10-15 HP, these engines may be compact. But for 80-100-200 HP, they will be bulky compared to the width and height of inline engines.
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Old 18th May 2015, 22:03   #10
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Default Re: Explained! The different types of Petrol Engines (Inline, Flat, V etc.)

@theMAG:- The points for the I4 are placed below that of the I6. Editing required.

Number of points need to be amplified. Some can be debated.

@Rahul Bhagat: Popular early aircraft engines were rotary (as opposed to radial).

Regards
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Old 18th May 2015, 22:19   #11
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Default Re: Explained! The different types of Petrol Engines (Inline, Flat, V etc.)

Sutripta,

1. The points are commonly categorized for inline engines, not gathered under inline 6 specifically.
2. Please feel free to add further insight to the discussion, by all means. This thread is intended to collaborative.

Last edited by theMAG : 18th May 2015 at 22:23.
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Old 19th May 2015, 23:25   #12
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Default Re: Explained! The different types of Petrol Engines (Inline, Flat, V etc.)

http://liquidpiston.com/

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There are many prototype rotary engines running currently and Liquidpiston's X Mini is a 70 cubic centimeter gasoline powered rotary four-stroke engine prototype based on HEHC thermodynamic cycle and patented engine architecture.
Explained! The different types of Petrol Engines (Inline, Flat, V etc.)-liquidpistonx1.jpg
To date, the X Mini prototype has demonstrated 3.5 horsepower (net indicated) at 10,000 RPM and the ability to run steady state with air-cooling.
When mature, the engine is expected to weigh 3 pounds, produce over 5 horsepower at up to 15,000 RPM, and be over 30 percent smaller and lighter than comparable four-stroke piston engines.
Explained! The different types of Petrol Engines (Inline, Flat, V etc.)-hehc-cycle.jpg
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Old 21st May 2015, 04:35   #13
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Default Re: Explained! The different types of Petrol Engines (Inline, Flat, V etc.)

Quote:
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4. Rotary/Wankel engine
Great thread, Mod! Rating it 5 stars. Thinking about the Wankel engine, Mazda and AutoPorn the first car that comes to mind is the Mazda Furai concept powered by an in-house R20B Renesis3 3-rotor Wankel engine churning out 450 horses at its best. Good things don't last though, eh? Sadly, the only one in the world got burnt during a test run.

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Image and News Courtesy: Top Gear Magazine
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Old 20th March 2016, 10:50   #14
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Default A noob's guide to nationalities of cars and their engines

We all keep on hearing different things like a lazy fat torquey american V8 "motor' or a finely honed high revving japanese engine. We read stories about how people have made 1000hp from a 2 liter Mitsubishi Evo X engine and wonder why exactly do you need a 8l W16 Buggatti Veyron engine when Evo can do the job. And you must be wondering why specialists charge you to take your own engine parts, get them forged and fix them back to get more power. And if it makes more power, why do the manufacturers do not do it themselves. And why would no japanese manufacturer provide a big fat 7.4L V8 and why would no american manufacturer make a harmonious 2L I4 engine and why are american designed cars XL sized and why japanese cars always have spot on ergonomics. For that you need to take a lesson of history.

Introduction

First things first. The car companies are run by the Accountants. Not by engineers, not by innovative leaders, not by exuberant businessmen, not by the passionate designers. No, a car company is run by the accountants. And so, the accountants see which model and type of car is making a lot of money and they make their own copies of cars. You should have obviously seen the trend by now. I mean Renault Duster was a hit. And all of a sudden, there is Suzuki S-cross, Vitara Brezza, Hyundai Creta, Ford Ecosport, Fiat Avventura, Toyota Liva cross, Hyundai i20 active etc...

You get the point. The same is with engines. In america back in the 50s, one of the big giants of american industry made a fast going car. And the formula he applied for that is simple. He knew that the higher he would price the car, the lower the chances of selling. So, he got a cheap, ordinary but big engine from a truck or something, plonked it into a normal car and the car went faster. The americans were very pleased with themselves. And the trend followed. Every car started boasting how big the engine size is. And so, in America, now it has become a superstition and they believe that only big engines make big power. And so, they make fun of Honda which gives them small engines with good power. And that is the reason why you will always find big and heavy engines in America. The engines wont be hi-tech or particularly refined, they will just be big and bulky and every sportscar they make will be accessible even to the blue-collared employee. And so, the americans can't and wont make a dignified and exquisite gentleman's car with a big price tag.

In the educated world of Europe, they had motorsport. And then the Austin Mini came. It revolutionized rallying. It did not have any respectable power figure for the engine. But because of the lightweight, when all the other cars would slow down to take a corner, the mini went flat out and it won the World Rally Championship. And obviously, the fame of Mini made fat profits for companies. So, all car companies in Europe started copying the formula. Money is not an objective. Just make the car as lightweight as possible, give it a perfect chassis balance and weight distribution and put an engine that would not upset the balance much. So, they made lightweight engines with the most perfect and accurate parts to extract as much power as possible. And people were ready to put cash into the pit for that. And so you will always find that european cars are unnecessarily expensive and built with very less tolerances. So, take a typical VW or BMW or Merc of today, forget a service or an oil change and see what happens. Blam, boom and a big bill. Why? Because the europeans only care for making the car engine as light and tight with as little tolerances as possible. And so, the british car industry ended when they could no longer make reliable cars. And the germans too are failing because one negligence and the car is ruined forever. And hence no one has a german car for more than 5 years.

The japanese are very disciplined and efficient. And naturally the world progressed towards more speed and more power. They looked at the american market which wanted power and the european market which wanted speed and agility through the corner. So, they decided that they will make both possible. With their intellectual prowess, they made a "Godzilla" (quite literally). They said, well good cornering speeds means AWD and electronically managed power distribution for the most efficient use and because of the added grip, they can add bigger engines with more power. And now, even when the power part came, they got the best out of the engines with precision engineering. They saw all the others blow up their engine in the corners because with high cornering forces, all the engine oil goes into one side of the engine. And without lubrication, the engine would die. So, they built some resistance into their engines. Then they saw people taking ages to remove every other part to access one bolt that holds the piece together. So, they made their cars with bolts in one place so that you no longer need to open the whole engine up just to change the oil filter. Hence japanese cars are just perfect. The only problem with them is that the japanese are good at perfecting things. To make an entirely new thing, they have to turn to other people.

Adding some science

In the world of engineering, there are terms like power and torque etc. Let me explain them to you so that we can get into the matter.

TORQUE: It is an engineering term used to describe how much force is exerted at a certain distance from the center.

So, the force exerted by the engine is actually torque. The ordinary citizen thinks that the engine is powerful when the power is high but the so called powerful engine is when the torque is high.

So, engine pulling capacity is torque.

POWER: It is an engineering term used to describe how much energy is being given per second.

Power = Torque x Angular velocity

The point to highlight is that the power can be high because the torque is high or the power can be high when the speed of rotation is high. When the speed of rotation is high, that small torque is given many times per second giving out more power.

In other words, power is how fast the engine can pull the load.

Theory of an engine

For the sake of this discussion, the only thing you need to know is that in an engine, the petrol and air mix up inside the engine volume and explode giving out energy. So, when you have a small engine, less petrol and air is mixed and so less power and less torque is made. This is a simple engine. To overcome the shortage of power, there are many things people do.

1. Increase the size of engine. You guessed it right. The americans. What they do is they make a big engine and so more petrol and air inside the engine, more energy comes out (more torque). So, american engines are big and give more pulling capacity. The engines pull more load and so they add big gears. And so, with big gears, the car goes fast. But, the engines do not speed up so fast. So, an american engine wont respond well to accelerator inputs. When you poke the accelerator of a japanese car, the revvs climb upto 2000rpm whereas in an american car, they climb by 500rpm. The upside of making american engines is that, you don't need sophisticated manufacturing processes to make a powerful engine. Just make the parts bigger.

2. Increase the speed of engine rotation. The europeans and japanese engines. What they do is that they let the engines be small but increase the rpm to increase power output. The problem with engine is that, at higher rpm, the engine vibrations are higher and the engine risks exploding. Hence they use costly manufacturing process to make the same metal harder. Sometimes, they even resort to forging. So, now, the engine pulls the same weight but much faster than others. That is "high revvving engines". The problem of this type of engine is that, when you are climbing a slope, the force required increases and so does the torque. But these engines have low pulling power because in the end, the engine size is small, so smaller bang and smaller pulling power (torque). Hence, cars with smaller engines struggle to climb up a slope even though they have more power. And the torquey big engines with low power output can blow past by. Also, it is expensive to make stronger parts for the small engine and so the engines made like this are expensive.

3. Supercharging/turbocharging. In supercharger, a compressor connected to the engine via a belt compresses air and supplies it to the engine. This means that more air and petrol comes into the chamber. So, the small engine is acting like a big engine. And so obviously more torque. And to handle more forces, stronger parts. And hence, you can make a small engine with more pulling power as well as more power and high revving. The parts just need to be super hard. And that is not feasible on normal cars. So, the sacrifice the high power bit and stick to high torque bit only.

In turbocharger, there is a turbine which taps the energy from flow of exhaust gases and uses that energy to compress incoming air into the engine. So, even here the small engine is acting like a big engine, same like supercharger. The problem with turbocharging is that, when you press the accelerator pedal, some air comes into the engine and speed increases. This pushes the turbine faster and so more air comes in and so the engine speed increases. This process takes time and so the turbocharged engine is not so immediately responsive. Floor a turbocharged engine and a Naturally Aspirated engine of same specifications and the NA engine will pick up revvs faster.

One more problem with turbocharged engine is that the turbocharger works in proportion values. So, if you are running at 4000rpm, the compressor give you a lot of air and a lot of compression than the optimum value. And so, at higher rpms, there is mad speed and pickup. But there is a crossover point (I made up the term). At the crossover value of 1800 rpm, the compression is in constant proportion to what the engine needs. So, at 1800 rpm, engine will be getting the amount of air that it requires. So, it is working like a normal engine. But at 1000rpm, the air blown in is proportionately low. So, at 1000 rpm, the air blowing in is less than what the engine needs. Hence the engine is out of breath and powerless.

The advantage of turbocharger is that since it is using the energy from the exhaust gases which otherwise goes waste, hence the energy of engine is used more effectively and so mileage of engine increases. Opposite to supercharged engine. In a supercharged engine, since it is tapping energy from the engine itself, it is less efficient. But as soon as you poke the A pedal, it revvs.

Last edited by aveemashfaq : 20th March 2016 at 17:21.
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Old 8th May 2017, 06:56   #15
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Default Re: Explained! The different types of Petrol Engines (Inline, Flat, V etc.)

As mentioned earlier in the thread, the Duke axial piston engine rings a bell for many of us who are familiar with hydraulic power systems. I found the link - which has probably been updated & now has cutaway videos - which now gives a fairly graphic and more comprehensible presentation.

I came across this in the usual way, while browsing the net. And what caught my eye was the axial piston bit. As marine engineers, most of us are familiar with axial piston swash-plate type of variable-delivery pumps used for marine steering gear systems. That a similar (well, almost) principle could be used in reverse as a prime mover, proved to be irresistible. I am giving a link to the site with cutaway videos showing the operating mechanism. Quite fascinating. One weakness I felt (after a cursory view of the video) appeared to be the matter of providing gas tight sealing where the pistons slides across the swash plate (or stationary head ring) from one port to the next. Rather like the problem faced in the Wankel rotary engine, where sliding vanes did not provide long-lasting seals.

http://newatlas.com/duke-engines-axial/33631/

Last edited by shashanka : 8th May 2017 at 06:57.
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