***Subaru Diesel??!

[Chip]

IMO the long stroke & long connecting rod requirements of a diesel design run contrary to the width constraints that currently force Subaru to use the shortest stroke and shortest rods possible in their gasser engines.

 

 

The difference in stroke between a Diesel and Gas engine is actually quite small.

Example. VW 1.9T,(gas)..stroke = 3.65 in.

VW TDI = 3.76 in.

[blitz]

The difference in stroke between a Diesel and Gas engine is actually quite small.

Example. VW 1.9T,(gas)..stroke = 3.65 in.

VW TDI = 3.76 in.

Let' be sure that it's understood that BORE/STROKE ratio was my original point (although for expediancy I didn't specify).

 

Subaru EA-81

Bore - 3.62

Stroke - 2.64

Ratio - 1.37

 

VW TDI 1.8

Bore - 3.19

Stroke - 3.76

Ratio - .85

 

In order to minimize package width, Subaru boxers are ideally OVERSQUARE.

In order to reduce flame-travel distance (diesel combustion speed is naturally slow compared to gasoline), diesels are ideally UNDERSQUARE.

 

Same goes for ROD/STROKE ratio.

In order to minimize overall package width, Subaru boxers ideally have short rods relative to their stroke.

In order to slow down the piston speed away from TDC(to accomodate the slow combustion speed), diesels ideally have long rods relative to their stroke.

 

Therefore I re-iterate the thrust of my point which is that the ideals for good diesel engine design are at odds with the packaging requirements for an automotive boxer configuration.

 

In fact the packaging requirements force Subaru to build an engine which pushes the envelope for what might be considered "ideal" for even a gas engine.

[blitz]

While researching my reply above, I hit on some info that might be valuable to some on this board. For anyone that wants to cut, paste, & save, here it is: (it's Bore/Stroke/Displacement first in inches, then in metric.)

--------------------------------

 

Four-Cylinder Subaru Engines

 

--------------------------------

 

{2.835 / 2.362 / 59.6} / {72 / 60 / 977}

These are EA-52 engines used in 1966-1970 Subaru automobiles.

 

 

 

{2.992 / 2.362 / 66.4} / {76 / 60 / 1089}

These are EA-61 engines used in 1969-1971 Subaru automobiles.

 

 

 

{3.346 / 2.362 / 83.1} / {85 / 60 / 1362}

These are EA-63 engines used in 1978-1980 Brats and 1977-1989 sedans.

 

 

 

{3.622 / 2.362 / 97.4} / {92 / 60 / 1595}.

These are EA-71 engines used in 1975-1976 sedans.

 

 

 

{3.622 / 2.638 / 108.7} / {92 / 67 / 1782}.

These are EA-81 and/or EA-82 engines used in 1980-1989 Brats, 1985-1991 XT coupes, and 1980-1999 sedans. They have the same bore and stroke as the six-cylinder ER-27.

 

 

 

{3.461 / 2.953 / 111.1} / {87.9 / 75 / 1820}.

These are EJ-18 engines used in 1989-1996 Impreza models.

 

 

 

{3.622 / 2.953 / 121.7} / {92 / 75 / 1994}.

These are EJ-20WRX engines are used in 2002-present WRX sedans.

 

 

 

{3.815 / 2.953 / 135.0} / {96.9 / 75 / 2212}

These are EJ-22 engines used in 1990-1994 Legacy models and the 1999-2001 Impreza. They have the same bore and stroke as the six-cylinder EG-33.

 

 

 

{3.917 / 3.110 / 149.9} / {99.5 / 79 / 2457}

These are EJ-25 engines used in 1999-present Forester, Impreza RS, Legacy, and Outback models; 2001-present SUS models; and 2003-present Baja models.

 

---------------------------------------

 

Six-Cylinder Subaru Engines

 

---------------------------------------

 

{3.622 / 2.638 / 163.1} / {92 / 67 / 2672}

These are ER-27 engines used in 1988-1991 XT sports coupe. They have the same bore and stroke as the four-cylinder EA-81 and EA-82.

 

 

 

{3.512 / 3.150 / 183.1} / {89.2 / 80 / 3000}

These are the EZ-30 engines used in 2001-present Legacy and Outback models; also known as the H6-30 engine.

 

 

 

{3.815 / 2.953 / 202.5} / {96.9 / 75 / 3319}

These are the EG-33 engines used in 1991-1997 SVX sports coupe. They have the same bore and stroke as the four-cylinder EJ-22

[blitz]

Here's a cut & paste from a diesel engine form that makes the point more elequently than I:

 

------------------------------

 

"Lets look at one place where an I6 has an advantage: stroke and rod length."

 

"It is a well known fact that diesel fuel is a relatively slow burning fuel, thus the need to use fancy high pressure injection systems and high compression ratio engines to get it to burn properly."

 

"Engines with longer rod to stroke ratios make the burning of diesel easier to do because the piston stays near TDC for a longer period of time, holding the combustion process in a smaller space and keeping it under more pressure. This improves combustion and efficiency."

 

"It also turns out that having a bore to stroke ratio of less than one (PSD is roughly one, Duramax about 1.2, Cat 3056 is 0.8 ...) really helps efficiency because it keeps the combustion chamber small during combustion and it makes more torque for a given cylinder pressure. It also scavenges better."

 

"Usually, this is ofset by a slower engine RPM, but to date the diesel V8s are not running higher redline RPMS than the I6s. I think that the short rods and short strokes of the PSD/Duramax cause the combustion efficiency to go to hell when the RPMS climb. (I'm speculating here.)"

 

"Thus, the long rod/long stroke arrangement of an I6 is considered beneficial by some diesel manufacturers."

 

"Unfortunately, it is quite difficult to build long stroke, long rod V8 diesel engines because the engine gets WIDE really quick. Consider this: the Cat 3056 is about 23 inches from crankshaft center to valve cover. (It has a 5 inch stroke.) If two such cylinder banks (3054) were joined to make a 90 degree V8, (8 litres) the engine would be about 32 inches wide ! (Actually wider, due to exhaust manifolds, etc.)"

 

"It is my guess that the Duramax is the configuration it is (short stroke, V8) so that it would fit into the engine compartment on the GM trucks without changing the bodywork."

[Scottbaru]

"It is a well known fact that diesel fuel is a relatively slow burning fuel, thus the need to use fancy high pressure injection systems and high compression ratio engines to get it to burn properly."

I thought the high compression was what made a diesel diesel? Couldn't you burn all kinds of fuel by compressing and heating it enough? Isn't diesel fuel slower burning to control the rate of expansion of the cylinder?

 

"Engines with longer rod to stroke ratios make the burning of diesel easier to do because the piston stays near TDC for a longer period of time, holding the combustion process in a smaller space and keeping it under more pressure. This improves combustion and efficiency."

Isn't the time a piston lingers at TDC just a question of engine rpm? Longer lingering at lower rpms? What's a longer rod have to do with it? If I had three-foot piston rods I'd still have the same stroke wouldn't I? The smaller space is just the chosen geometry of the engine. I don't get this part. I know diesels put out more power at lower rpm, didn't know why.

[Hondasucks]

I thought the high compression was what made a diesel diesel? Couldn't you burn all kinds of fuel by compressing and heating it enough? Isn't diesel fuel slower burning to control the rate of expansion of the cylinder?.

 

Right, diesel engines work on Bohls law that states that a gas will get hotter as it is compressed. Take air and compress it 23 times and it gets hot enough to ignite the diesel fuel. That;'s why they are called a compression ignition engine. I've got a diesel in my 92 Ram, got 14.5 coming out here from Oregon loaded down + towing a trailer with my Subie on it, try doing that with a gas truck! (My grandfather gets 11 MPG UNLOADED with his 460, I get like 17 back home unloaded, and he gets 7 loaded and I get between 14 and 16 depending on what I'm towing and where...)

[LPGsuperchargedBrumby]

just reading through this thread give me the feeling that some ppl are a bit set against diesels due to bad experiances with the older US domestic diesels.

 

im in New Zealand where about 40% of light vehicals are diesel and it always surprises me to hear (from america mainly) the same old complaints about noise low rpm redline and lack of power compared to a petrol engine.

 

nissan produced a motor called the LD28 a 2800cc 6 cyl that redlines at 5000rpm for the early'r versions and 5500rpm for the later ones produces 100hp NA (turbo version made alot more) and does't sound bad ,actualy sounds sounds real smooth and throaty if the right exhaust on it. and it gets 35mpg in something with the aerodymamics of a brick

 

how do i know? i got one in my work truck and wouldn't swap it for anything( exept maybe a dodge viper motor )

[Tiny Clark]

About the only place diesel is more expensive than gas is in the US. It is the cheapest fuel at German pumps.

 

Diesel prices went up to coincide with the advent of diesel cars being brought into the US. The truckers especially loved this.

 

Diesel is used in cargo planes, it's called jet fuel, which is basically diesel with additives. Many cargo aircraft are turboprops.

 

I've driven several cars over here with diesels, and quite frankly, I couldn't hear them any more that a regular engine while up and running. That Audi 1.8TD kicks rump roast.

[KStretch55]

Jet fuel (Jet A, JP8) is much closer to kerosene. It's considerably thinner, more volatile and cleaner than diesel.

[blitz]

I thought the high compression was what made a diesel diesel? Couldn't you burn all kinds of fuel by compressing and heating it enough? Isn't diesel fuel slower burning to control the rate of expansion of the cylinder?

Jeez, I don't even know where your going with all that, you can research it if you'd really like to know. My simple point being made is: diesel combustion IS slower than gas combustion (flame-travel). It wouldn't be impossible to build an ultra short-stroke/short-rod diesel that started and ran, it's just that the associated geometry needs to be accomodating if the high efficiency of the diesel is to be maintained.

 

That quote you attributed to me isn't my quote. It's someone elses.

 

Isn't the time a piston lingers at TDC just a question of engine rpm? Longer lingering at lower rpms? What's a longer rod have to do with it? If I had three-foot piston rods I'd still have the same stroke wouldn't I? The smaller space is just the chosen geometry of the engine. I don't get this part. I know diesels put out more power at lower rpm, didn't know why.

It works like this: Starting at TDC, the piston is standing still, but by the time it's halfway down the bore it's at it's maximum speed.

 

The effect of rod length to stroke ratio is manifested in the rate of acceleration of the piston from it's standing start at TDC towards it's top speed halfway down the bore. With a shorted rod, the piston makes more sudden movements away from TDC during the critical first part of the stroke, which gives the piston a greater tendency to outrun the flame-front as RPM's climb. This is especially problematic with a slow combustion process like a diesel.

 

If you were to chart the piston movement as a graph, you'd end up with a sinusiodal shape. The specific shapes of of the sinusiods will change as the rod/stroke ratio is changed.

 

Also that second quote wasn't mine either.

[Scottbaru]

That quote you attributed to me isn't my quote. It's someone elses.

 

If you were to chart the piston movement as a graph, you'd end up with a sinusiodal shape. The specific shapes of of the sinusiods will change as the rod/stroke ratio is changed.

 

Also that second quote wasn't mine either.

Sorry, I just cut-n-pasted so I could ask specific questions. All pistons constrained to a rotary crank follow the same sine wave shape, it can't be changed. A tiny crank running at high rpm will have exactly the same piston speeds and accelerations as a huge one at low speed, but travelling shorter distances in less time. So a smaller crank would mean shorter stroke and less dwelling at the top, not good for a diesel. I know rods are usually no longer than necessary, and so follow the crank size, but not necessarily. I still don't get why rod length is figured in at all.

[NorthWet]

just reading through this thread give me the feeling that some ppl are a bit set against diesels due to bad experiances with the older US domestic diesels.

 

im in New Zealand where about 40% of light vehicals are diesel and it always surprises me to hear (from america mainly) the same old complaints about noise low rpm redline and lack of power compared to a petrol engine.

 

nissan produced a motor called the LD28 a 2800cc 6 cyl that redlines at 5000rpm for the early'r versions and 5500rpm for the later ones produces 100hp NA (turbo version made alot more) and does't sound bad ,actualy sounds sounds real smooth and throaty if the right exhaust on it. and it gets 35mpg in something with the aerodymamics of a brick

 

how do i know? i got one in my work truck and wouldn't swap it for anything( exept maybe a dodge viper motor )

I am not against diesels, just illustrating that in the USA we don't, as a society, deal with diesels in a rational manner. Consumers ignore diesels because they are fussy, noisy, smelly, underpowered, and more expensive compared to gasoline-powered engines. We, as a group, do not want to deal with having to wait to start our cars, having to search to find someplace to buy fuel, smell up the house when we start the vehicle in our garages, smell our own exhaust while idling on the highway or while waiting to pick up our kids, hear the engine running at any time whatsoever, get outaccelerated by econoboxes, or have to get our oil changed regularly.

 

However, just let the cost of gasoline rise and all of a sudden everybody is talking diesel (I am not referring to just the people in this discussion, but our society in general). All those "inconveniences" evaporate so that we can "save" a penny per mile. Never mind that there is no consumer-level demand for diesel passenger vehicles in the USA, we want something NOW! So, in the past our automakers have decided not to spend the years needed to properly engineer a diesel engine and instead just slap together something based on an SI engine. We rush out to buy it, discover it is real cr*p, and p*ss and moan about it for decades. In the mean time, the price of gasoline drops a little and diesel increases a little, so that once again there is parity. Demand for diesel drops to nil again, and we continue on our consumer ways. Status quo ante.

 

There are some domestic diesel engines in the USA market, but they are meant to be truck engines. I also consider most of them to be used in "boutique" applications, ones where the owners wanted to have the cache of a diesel but don't really need it. Example: My best friend bought a Dodge pickup truck with the Cummins Turbo Diesel option, though he doesn't tow or haul anything. He wanted it because he used to be a long-haul trucker and wanted the ambiance of a direct-injected diesel; he wanted the noise and the smell, because it brought back good memories. Never mind that the engine option was an additional US$8000!!! That is above and beyond what a medium-displacement V8 would have cost in this truck. There is no economic rationale for his choice; it is just what he wanted.

 

In general, diesel passenger vehicles in the USA are fads, brought in by changing fuel prices or social conscience. IMHO, they fall into the same class as electric vehicles and hydrogen power. We have no installed base for mass diesel vehicles, and there is no social engineering that would encourage its use.

 

CI engines can last longer than SI, but most of that is because they are built more sturdily, not because of any inherent advantage to diesel (other than possible cylinder washing on a badly tuned SI). Build a good SI engine and it will last, too. (...subaru...) There is no market in the USA for durable engines; we have learned that we don't want to own a car longer than 3 years. Our V8s could easily last a million miles before the cylinders and rings wear out, but there is no econmic incentive to build them that way.

 

CI gets its greater fuel mileage because of greater energy density in diesel fuel, plus the greater thermal efficiency conveyed by its higher compression. That higher thermal efficiency also equates to higher NOx emissions, one of the most difficult to control. It can also have a real problem with particulate emissions.

 

Not "any" fuel can be used in a real-world CI engine. The fuel (or some significant portion of it) must have a cetane rating that will allow it to ignite given the attained compression heating. Using the diesel injection as an ignition source can help utilize other fuelse, such as propane.

 

Flame-travel has little to do with combustion rate in a diesel. The flame does not travel, it spontaneously occurs at the point of mixing between fuel and oxygen. So the practical restraints on combustion speed involve injection speed and fuel atomization, plus combustion chamber design (pre-chamber vs. direct injection and such) and turbulence.

 

Speaking of pre-chamber vs direct injection, this has a large effect on noise... and efficency. Consumer diesels tended to have pre-chamber type heads, which significantly reduced the sounds of combustion, but sacrificed efficiency. Commercial diesels are all about efficiency and reliability, so they are typically (exclusively?) direct injected.

 

I have no doubt that Nissan can and has produced very good diesel engines. They were fitted in several vehicles here during the 80's. They have a real commercial market for their product, with the incentive to do it right. No such market exists for USA domestic makers.

 

Regarding MPG, my 77 Dodge manages 14 MPG while loaded with 1ton+ and towing a car hauler with my Datsun on it, including going through some moderate passes (3000+ feet). This is with a clapped-out gas V8 that has at least one dead lifter. True, it only gets 14 MPG empty towing nothing on the flat, but that is the way US trucks were setup. Engine displacement and factory tune (trucks were jetted richer than cars) are major factors for truck fuel efficiency.

 

Thanks to KStretch55 for correcting the Jet-A issue. Turbines are also continuous ignition, not compression ignition. (nit, nit, nit)

 

I am not trying to put down diesels. I just do not believe that they are a viable option in the USA now or in the near future. As a society, we love to jump on bandwagons, but eventually we will slip off and climb back into the comfort of our SUVs. I think that the greatest hope we have to wean ourselves from guzzling fuel is the hybrid internal-combustion/electric vehicles. But I think it will take a real, sustained economic disaster.

 

"Tomorrow! Tomorrow! I love ya, tomorrow! You're only a tank away!!!"

[blitz]

Scottbaru, I've explained it best I can. I'll suggest that you do some actual research on the subject of Rod/Stroke ratio before claiming it has no effect on piston movement or engine performance. Here's something to get you started. Be careful not to let any of the facts get in your way.

 

--------------------------------------

 

The ratio between the connecting rod length and the stroke length of a motor greatly affects the way it performs, and how long it lasts. This ratio can be calculated as follows:

 

Ratio “n” = Rod Length ÷ Stroke

 

The rod’s length is measured (for this purpose) from the center of the piston-pin opening to the center of the big-end bore, not overall. There is a small range of ratios for most conventional piston engines: the rod is between roughly 1.4 and 2.2 times the stroke length. It’s not possible for the rod to be the same length as the stroke, and rods much longer than twice the stroke make the motor very tall, and are not practical for most purposes (although used for racing).

 

The rod angle must not encourage excessive friction at the cylinder wall and piston skirt. A greater angle will occur by installing a shorter rod or by increasing the stroke. A reduced angle will occur with a longer rod or a shorter stroke.

 

If the rod length is decreased, or the stroke is increased, the “n” ratio value becomes smaller. This has several effects. The most obvious is the mechanical effect. Motors with low values of “n” (proportionately short rods or long strokes) typically exhibit the following characteristics (compared to high “n” motors):

»

 

physically shorter top-to-bottom & left-to-right

»

 

lower block weight

»

 

higher level of vibration

»

 

shorter pistons, measured from the pin center to the bottom of the skirt

»

 

greater wear on piston skirts and cylinder walls

»

 

slightly higher operating temperature & oil temperature due to friction

 

---------------------------------------------------

 

There are also differences in how the motor breathes:

 

----

 

intake vacuum rises sooner ATDC, allowing bigger carburetors or intake port runner & plenum volumes to be used without loss of response

»

 

on the negative side, a small or badly designed port will “run out of breath” sooner

»

 

piston motion away from BDC is slower, trapping a higher percentage of cylinder volume, making the motor less sensitive to late intake valve closing (hot cams)

 

----------------------------------------

 

Spark advance is also affected:

 

----

 

earlier timing (more advance) is required, as the chamber volume is larger (piston is farther from TDC) at the same point of rotation

»

 

the motor may also be less knock-sensitive, as the chamber volume increases more rapidly ATDC, lowering combustion pressure (this is useful for nitrous & supercharged motors)

 

-----------------------------------

 

Effects of Long Rods

 

----

 

Pro:

»

 

Provides longer piston dwell time at & near TDC, which maintains a longer state of compression by keeping the chamber volume small. This has obvious benefits: better combustion, higher cylinder pressure after the first few degrees of rotation past TDC, and higher temperatures within the combustion chamber. This type of rod will produce very good mid to upper RPM torque.

»

 

The longer rod will reduce friction within the engine, due to the reduced angle which will place less stress at the thrust surface of the piston during combustion. These rods work well with numerically high gear ratios and lighter vehicles.

»

 

For the same total deck height, a longer rod will use a shorter (and therefore lighter) piston, and generally have a safer maximum RPM.

 

----

 

Con:

»

 

They do not promote good cylinder filling (volumetric efficiency) at low to moderate engine speeds due to reduced air flow velocity. After the first few degrees beyond TDC piston speed will increase in proportion to crank rotation, but will be biased by the connecting rod length. The piston will descend at a reduced rate and gain its maximum speed at a later point in the crankshaft’s rotation.

»

 

Longer rods have greater interference with the cylinder bottom & water jacket area, pan rails, pan, and camshaft - some combinations of stroke length & rod choice are not practical.

To take advantage of the energy that occurs within the movement of a column of air, it is important to select manifold and port dimensions that will promote high velocity within both the intake and exhaust passages. Long runners and reduced inside diameter air passages work well with long rods.

Camshaft selection must be carefully considered. Long duration cams will reduce the cylinder pressure dramatically during the closing period of the intake cycle.

 

------------------------------

 

Effects of Short Rods

 

----

 

Pro:

»

 

Provides very good intake and exhaust velocities at low to moderate engine speeds causing the engine to produce good low end torque, mostly due to the higher vacuum at the beginning of the intake cycle. The faster piston movement away from TDC of the intake stroke provides more displacement under the valve at every point of crank rotation, increasing vacuum. High intake velocities also create a more homogenous (uniform) air/fuel mixture within the combustion chamber. This will produce greater power output due to this effect.

»

 

The increase in piston speed away from TDC on the power stroke causes the chamber volume to increase more rapidly than in a long-rod motor - this delays the point of maximum cylinder pressure for best effect with supercharger or turbo boost and/or nitrous oxide.

»

 

Cam timing (especially intake valve closing) can be more radical than in a long-rod motor.

 

----

 

Con:

»

 

Causes an increase in piston speed away from TDC which, at very high RPM, will out-run the flame front, causing a decrease in total cylinder pressure (Brake Mean Effective Pressure) at the end of the combustion cycle.

»

 

Due to the reduced dwell time of the piston at TDC the piston will descend at a faster rate with a reduction in cylinder pressure and temperature as compared to a long-rod motor. This will reduce total combustion.

 

---------------------------------

 

Rod Ratio vs. Intake Efficiency

An “n” value of 1.75 is considered “ideal” by some respected engine builders, if the breathing is optimized for the design. Except for purpose-built racing engines, most other projects are compromises where 1.75 may not produce the best results. There will be instances where the choice of stroke or rod has not been made, but the intake pieces (carburetor, manifold, and head) have been selected. Some discretion exists here for making the rod and/or stroke choice compatible with the existing intake. The “n” value can be used to compensate for less-than-perfect match of intake parts to motor size & speed. The reverse is also possible: the lower end is done, but there are still choices for the top end. Again, the “n” value can be used as a correction factor to better “match” the intake to the lower end.

 

The comments in the following table are not fixed rules, but general tendencies, and may be helpful in limiting the range of choices to those more likely to produce acceptable results. Rather than specify which variable will be changed in the lower end, “n” values will be used. Low “n” numbers (1.45 - 1.75) are produced by short rods in relation to the stroke. High “n” numbers (1.75 - 2.1) are produced by long rods in relation to the stroke.

[Olnick]

Bravo, NorthWet. Very elegantly put.

 

Blitz and Scottbaru: WOW! I am absolutely blown away by the level of theoretical thinking in your Qs and As. Fascinating discussion.

 

The knowledge available on this board is astounding. Thanks all.

[KStretch55]

Very well put, Northwet. I have to agree.

[wintersubaru]

I know of an engine that will solve all these problems. Crysler had one ine the 60's and pontiac is working on it again.will burn anything liquid that will ignite and get at least 60 M.P.G. ITS CALLED A TURBINE! But thanks to big oil we may never see it in a car.

[Scottbaru]

Thanks blitz, that's probably all I could want to know on the subject. Hopefully I'll never have to design my own diesel engine, but if I do I may have more questions. Most of my experience with diesels is renting them overseas, and a few VW diesels over here. I don't set up the rentals, take what I get, sometimes I have to check if it is a diesel they're so quiet and smooth. Diesel cars use less fuel, if fuel prices go up again Americans will buy them.

 

Jet fuel is kerosene, that's why Air Force tankers are designated KC-135 and KC-10.

 

Turbine engines are a little tough to fit in cars, I haven't seen a lot about them lately. They're efficient in a fairly narrow rpm band, takes a heck of a transmission. And exhaust system. How big a catalytic converter would you need?

[subie94]

i was told about an article the other day from the local newspaper(new hampshires union leader)about this guy that has a car that ran on bio-diesel.well i guess he filled it up one day an spilled some on the ground.living in an area were bears are,the smell caught there attention an the bears basically tried to eat his car.plus he left the cap off so they must of had a field-day with his car

[BigMattyD]

I am not sure a turbine engine would be practical in a car,

 

 

(except for the Batmobile...)

 

They are loud, they need to run at high rpm to be efficient, which means some type of transmission has to convert the continuous high output of energy to a stop-n-go type of output. (The engine is wasting fuel when the car is not operating at a constant speed.)

 

Also, turbine engines are expensive, have exacting tolerances, and require professional maintenance. Also, it seems that they are difficult to scale down to the size required for a car. Making them larger does not seem to be as big an issue. That is one of the reasons we don't see small, inexpensive turbine engines in aircraft.

 

The smallest turbine engines are large, and expensive, require a higher level of technical skill to operate and maintain, and provide more power than required for a small aircraft (or cars.)

 

On the other hand, piston engines seem easy to scale down, think fo lawn mowers or hobby motors but reach a certain limit of practicality at very large sizes.

 

I don't have vast technical knowledge in this area, but these are just a few thoughts. Any professional advice from a turbine designer would be greatly appreciated.

 

Matt

 

P.S. (Don't expect to fix one yourself.)

[scoobyclimbs]

Just go to carls jr. and get greased by Paris! BIO-diesel.......yeah baby!!

[Tiny Clark]

Jet fuel (Jet A, JP8) is much closer to kerosene. It's considerably thinner, more volatile and cleaner than diesel.

 

But I believe diesel is closer to kerosene than gas.

 

I don't know why they can't use a very small 3 cylinder constant speed diesel motor, similar to what small sailboats use when caught "in irons", and use that to turn a generator, in turn using electric motors to drive the wheels.

 

Our new portable generators/light-alls run on this engine for hours using relatively little fuel.

 

 

 

 

 

'

[Scottbaru]

I think that's the direction the hybrids are going, haven't gotten to diesels driving the whole thing yet, although that seems perfect to a lot of people.

 

Trains use a diesel-electric system, and Saddam had a fleet of Bluebird Wanderlodges fitted that way for luxury desert cruising.

[LosDiosDeVerde86]

i don't know any answers to your questions... but... it seems to me that the amount of torque coming from as diesel would torque your little unibody in half if you pegged it. just a thought....

 

no. you dont see jetta diesels that look like prezles on the side of the road do you? just because it's diesel doen't mean its an 18 wheeler

[hooziewhatsit]

I don't know why they can't use a very small 3 cylinder constant speed diesel motor, similar to what small sailboats use when caught "in irons", and use that to turn a generator, in turn using electric motors to drive the wheels.

 

like this bus? http://www.trimet.org/environment/hybridbus.htm It's amazing the stuff tri-met is doing to reduce pollution, noise, recycle, etc.

 

I agree, I've been thinking about some kind of system like this for a while. Throw the generator & batteries in the back of a brat, electric motor up front, and drive on.

 

This is probably the direction most stuff is going to end up heading.

[Buddythedog]

Buddythedog said:

 

 

 

 

I'm having trouble with that math; doesn't seem right. Say a gas engined Subie gets 25 mpg. That's 800 gallons in a year, if we assume 20K miles a year. At $2.25 a gallon, that's $1800. Say a diesel VW gets 40 mpg (extra 15 mpg as stated above). That's 500 gallons of diesel. Even if diesel was only $2 a gallon (it's higher, right? I don't know ATM) that's $1000, for $800 a year savings, not anywhere near three large. If you drive fewer miles, or diesel is more comparable in cost to gas, then the savings go down from there.

 

Just trying to clarify.

 

Steve

My reply is that I'm an idiot. I was using the calculator on my Windows program.