why only piston cylinder engines.......

why the engines with piston cylinder arrngement so popular as compared to other type of engines........

Reply to
jas
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That's like asking why are there mostly jet engines on commercial aircraft... best, most economical for the job...

Reply to
fclaugus

As a philosophical basis you might want to read _Disturbing the Universe_ by Freeman Dyson, especially the chapter entitled "Clades and Clones," for an introduction to the evolution of technology.

That sort of engine has proved over time to be a manufacturable, durable, reasonably efficient way to turn practical automotive fuels into the amount of power that cars need, with startup time and demand variability that drivers demand, in a compact package. Actually, the particular arrangements most commonly used -- layouts and valvetrains and number and size of cylinders -- are fairly few in number, in passenger cars.

It is of course not by any means the only way of making wheels go 'round. All sorts of things have been tried: steam came and went; Wankels come and go. Turbines make some sense for big stuff that doesn't change speeds on the time scale that cars do (ships for instance) but even there you find piston engines; turboshafts have been tried in cars and it worked out only semisuccessfully. Now solid-state electronics enables hybrids to be pretty good (but the fuel-burning part still has pistons; ditto for the diesel-electric locomotive, which is configured the way it is because of difficulties in making clutches and gears for such huge power and the problems in getting such a big load started.) Pure electrics have been around since darned near day one of the automobile, and are okay for certain specialty uses, but the battery technology that could truly replace fuel engines in passenger cars remains elusive (trains, again, are a different story, as are trolley cars in some places, since you have exact control over where the extension cord goes). Fuel cells hold much promise, or so it looks if you stare at the crystal ball awhile, but they work best with fuels other than the now-ubiquitous gasoline...

But the ante in this game is pretty high -- both diesel and gasoline piston engines are really rather amazing in what they can do and how long they last and so forth -- and it'll take either a breakthrough by one of the rivals or a big change in the ground rules to displace them.

Reply to
Ad absurdum per aspera

The only other types I know of are turbines. Turbines are way too expensive for mass market. Pistons are easily made on any of several machine tools. Turbine blades are not easily machinable shape, plus materials need to be higher temperature materials which are not easy to machine. And you need far more turbine blades than you do pistons.

A couple of decades ago companies tried direct cast turbine blades. Had to be out of lower temp materials, which ended up with low fuel efficiency- not good in days of climbing fuel costs.

Reply to
Don Stauffer

Overall they haven't found anything better.

Reply to
« Paul »

because their easy to make maintain and cheap.. from a design and cost of manufacturing point of view their the best we got. one day we will all be fuel cells and electric but thats a long way off.

Reply to
pigcharger

I disagree. Yes, this is true, but the reason that they are still around is that other competitive direct fuel-burning engine architectures have

*universally* proven less efficient to operate in the automotive application.

That's a fundamentally different animal- one that I would call "indirect fuel-burning" at best. The real things to compare to piston engines are turbines (gas and steam), reciprocating steam engines, and wankel engines.

Reply to
Steve

There are many reasons that we have stayed with the piston engine for converting one form of energy to another. Inertia is somewhere on the list I'm sure. But close to the top of the list is it's operating flexibility, or the ability of the piston engine to perform at a wide range of speeds and to change speeds quickly. Other designs such as the turbine and stirling are more suited to constant speed applications. The electric motor probably exceeds the operating flexibility of the piston engine but it suffers because efficient ways of providing an adequate supply of energy are still being developed.

Reply to
John S.

as stated by others, so far, it's the best kid on the block.

I want a wankel (mazda) but don't have room for it at the present time, they have always - amused me.

I read in the news where there was a motor manufacturing facility being built in china -

for world-wide distribution of - auto engines. Not sure if it was wankel, doesn't seem feasible - now.

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Reply to
fiveiron

But the reason automotive gas turbines have been inefficient is that they are constrained by affordable and machinable turbine blades. Military and modern civil aircraft turbines are getting VERY efficient, but they run 20+ CR and VERY high turbine inlet temps. These temps would destroy affordable blades in minutes.

Turbines can be quite efficient, but only at the expensive of high TIT, corresponding to fancy cooled blades made of exotic materials.

Steve wrote:

Reply to
Don Stauffer

So why isn't GM and Ford funding development of low-cost superalloy machining techniques?

--scott

Reply to
Scott Dorsey

There are also the "minor" factors such as high(er) inlet temperature near ground level, thermal cycling, noise and exhaust gas temperature.

The last can be ameliorated by running a compound steam cycle powered by the "waste" heat from the gas turbine combustion cycle. This also improves total thermodynamic efficiency to be comparable with IC engines; but with greater package volume.

That shouldn't matter so much with heavy haulage vehicles and the duty cycle of them is better suited to has turbine deployment anyway.

As for machining, "cheap" turbine blades can be made from a variety of materials that are ostensibly difficult to machine; either by lost-wax investment casting, or in the case of ceramics; growing the material to the correct shape.

But one doesn't need materials frequently used in aircraft gas turbines: At the end of WWII, due to lack of exotic alloys, Germany was making cheap gas turbine blades from folded sheet alloy steel, cooled internally by airflow bled from (IIRC) the first stage of the compressor. Such blades had a rated life of about 100 hours; about

200 flights; but other parts of the engine usually failed before the turbine blades. The technique of internal cooling has since been re-invented at least twice.

Steel is by itself a good thermal insulator is no panacea. The stress on the outer "skin" of a hollow blade will be under compressive stress, trying to stretch its cooled core. Improving the thermal conductivity (or just the wall thickness) reduces the stresses and the skin temperature.

Various surface treatments can help to reduce the peak temperature experienced by the steel of the structural blade. It should be obvious that the surface treatments need to be applied with the blade at about operating temperature to minimise the stress imposed on the core and the surface coat. However, when the blade cools an internal "tension" is likely to prevail, making for a situation where a fracture could be "explosive". One mode of failure is for the surface to flake-off, leaving the unprotected steel exposed to the hot gases.

That doesn't matter in an aircraft because aircraft are subject to close mechanical scrutiny, often mandated. Put them into a car that might see a workshop every 2 years and run perhaps 1000 hours with

2000 full thermal cycles between cursory inspections and you have a problem.

A gas turbine for normal automotive use has to be tougher than one for aircraft. Even when maintenance is neglected, it has to have similar reserves of safety, strength and durability to an IC engine.

Reply to
Bernd Felsche

the present day gasoline engines for motor cars is apparently offering the most bang for the buck,

but conditions that are surely to come will require engine downsizing, as the trend has been of late.

the present day technology for gasoline engines is to be commended, it in itself has synergistic value that's unequalled.

Reply to
fiveiron

snipped-for-privacy@webtv.net wrote in news:7692-44621371-44@storefull-

3316.bay.webtv.net:

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check out this wankel type modern design to see what may be on the horizon. Fixed the many wankel problems and has a lot to appreciate. KB

Reply to
Kevin Bottorff

'cause they are both hurting financially. Also, this development has been going on for fifty years without success so far, and they may have concluded there IS no practical solution.

It used to be in the aerospace industry I'd read, every two or three years, of such a breakthrough, either a new material or a new ceramic coating method. NONE of these really worked- well, a few worked but are still so expensive they're only useful in military or expensive long range commercial aircraft.

Reply to
Don Stauffer

That is why hybrids hold so much promise. One big source of inefficiency on gasoline engines is throttling. Excessive throttling spoils efficiency.

Any car has two power requirements, average power, say to cruise at constant speed at some cruise MPH, and peak power- the desired acceleration rate. A PROPER hybrid should have the IC sized for the average power required, and the electric motor sized for the difference between peak and average horsepower.

A proper hybrid is a series hybrid, in which case the engine is either on or off, and never operates at partial load. So no throttle is needed.

Reply to
Don Stauffer

moral: hiway speeds governed with a cruise control is being frugal.

but at what steady topside hiway speed yields the most mpg?

Reply to
fiveiron

I have seen a number of studies stating between 50 and 55 mph for most modern cars.

Consider that it requires 36% more fuel to drive a given distance at 70 mph than at 60.

Reply to
Don Stauffer

Codswallop. You don't have to drive a *tank*.

My fuel consumption rises from about 5.5 l/100km to 5.7 l/100km on good, smooth pavement when speed is increased from 100 to 110 km/h

The most fuel-efficient depends on the vehicle, (including condition), the fuel being used, the load it's carrying, the road, traffic and weather conditions; and not least; the manner of driving.

It's not a fixed number.

You can save fuel by driving more quickly in summer because airconditioning sucks fuel dependent on the time that you're on the road and the heat load on the passenger compartment. Driving more quickly reduces the total amount of fuel required to keep the interior of the vehicle comfortable. That amount can vary from 0.5 to 3 litres/hour -- depending on the car, the weather and the setting of the fridge.

Reply to
Bernd Felsche

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