steel-on-steel friction is remarkly high, as much as 0.8 (compare to ~1 for good pneumatic tires). The problem with trains is that most of the total mass is contained in the trailing cars instead of the locomotive; it’s not pressing down on the locomotive’s drive wheels, and therefore not helping to create tractive force. So for a train with 100 cars and five locomotives, maybe 5% of the total mass is aiding in the development of traction. 5% * 0.8 = 0.04, so the fastest you’d hope to accelerate is about 0.04 g’s.
TL;DR, traction is an issue for trains, but not particularly because of the coefficient of steel-on-steel friction.
This is implausible. To my knowledge, ICE combustion efficiency (the % of chemical energy released as heat during combustion) is upwards of 98%; it’s difficult to get “much more” complete than that.
I appreciate and accept your engineer’s explanation of friction. However, it doesn’t change my point. Trains are big-ass hunks of mass and getting one rolling by spinning a couple of wheels necessarily requires those wheels to start out turning slowly. This is dramatically different from the situation in a passenger car. And the initial speed at which drive wheels turn has little or nothing to do with the ultimate speed the vehicle may attain.
As for “complete” combustion, I’m not talking about efficiency of energy extraction. I’m talking about the conversion of complex hydrocarbons into simpler compounds through an exothermic reaction involving oxygen. The gunk that comes out of the tailpipe of an IC car is a noxious brew of all sorts of incompletely-burned compounds. These are the compounds that turn city air funny colors and make it difficult to breathe. In large part this is due to the necessary speed of the combustion cycle in a cylinder and the limitation on amount of oxygen present in the fuel mix. In complete combustion, those original hydrocarbons would be oxidized down to CO2 and H2O. More like the flame on my gas stove. So having the flame from my stove boiling water or Freon in a steam boiler will produce far less pollutants than the IC engine in my present car.
So when we talk about tradeoffs in efficiency, perhaps steam should get credit for not contributing to pollution levels, and some costs of pollution mitigation might be credited to the steam side of the equation. (Neither steam nor IC, as I said before, changes the fact that burning hydrocarbons produces the greenhouse gas CO2.)
The main reason most steam locomotives start slowly isn’t any particular quirk of steam power itself; it’s that the vast majority aren’t geared. They’re direct-drive, and designed to work efficiently in a relatively narrow band of speeds and loads.
Passenger cars are geared- you start out in low gear, and shift repeatedly, letting the engine work more efficiently relative to the speed of the wheels.
I suspect a steam locomotive with a multispeed gearbox might be able to start a whole lot faster than direct-drive steam locomotives.
I discussed all that in my post #34, thanks. It was in reply to a contention that steam locomotives didn’t have gear boxes because “acceleration isn’t important”. I was pointing out that swift acceleration might or might not be important but it isn’t *possible *given the mass of trains and the small contact surface of the drive wheels.
You are confusing torque and power. Power is the product of torque and rpm.
Without a transmission, the engine rpm is always proportional to the speed of the car. So without a transmission, you can either have lots of torque and low top speed, or you can have high top speed and low torque. Transmission allows you to have both, and steam engines are no exception.
Personally, I do not see steam engine ever gaining a market share in cars. Their perceived advantages are simply not there.
As to weight, ICEs are always lighter than steam engines. As a simplistic proof, aircraft designers tried for the last 100 years to get the most power out of the lightest piston engine. Particularly military designers in 30s and 40s were almost free of conventional restrictions and came up with the wildest ideas. Yet the number of steam powered aircraft is tiny.
As to fuel flexibility, it has never quite worked out. If you are using liquid fuel, the system is always optimized for one kind of fuel. You can pour in something else, but only if you are prepared to accept a loss of performance and increased maintenance. A permanent modification, of the kind you suggest is equally possible with ICEs. Gasoline to LPG conversion used to be once somewhat common in Europe. Gasoline-to-ethanol conversion also requires little work, and diesels can be tweaked to burn a number of fuels.
Steam engines may produce fewer NOx emissions, since combustion takes place at lower temperature and pressure. However, burning something like diesel at lower temperature will increase particulate matter (PM) emissions. NOx is the one responsible for “funny” colors, while PM is the one responsible for respiratory illnesses.
As to incompletely burnt fuel, the amount in exhaust of modern engines is virtually zero (except for PM and while running at full load). The amount of gasoline that evaporates at gas stations and from you car’s fuel tank is a much larger concern.
I explicitly defined the parameter I was discussing, i.e. “the % of chemical energy released as heat during combustion”. It’s the same thing you were talking about: in a modern automotive internal combustion engine, about 98 percent of the energy locked away in the H-C and C-C bonds of a long-chain hydrocarbon molecule are released as heat. After that, there are a number of energy costs and inefficiencies that reduce how much of that ends up as crankshaft work:
-thermal losses to the cylinder walls
-theoretical limit of efficiency due to the finite expansion ratio (manifested as hot exhaust)
-friction losses
-pumping losses
-accessory drive losses (alternator, water pump, etc.)
What you call “gunk” coming out of an IC engine’s exhaust manifold is, in an absolute sense, pretty clean; it’s almost entirely CO2, H2O and N2. It’s just that we’re really fussy lately about getting it really clean. A lot of the “gunk” you’re referring to is oxides of nitrogen, which are unrelated to combustion efficiency; they’re a product of high temperatures plus excess oxygen. The remaining pollutants are mostly CO and some unburned hydrocarbons, but very little; the amount of energy you would get by completely oxidizing those two is pretty small, about 2% of the total energy that came in with the injected fuel. We denigrate that trinity (NOx, CO, HC) as “gunk” and work to reduce it further with emission control devices because even at those very small percentages, they are nasty environmental pollutants.
Simply not true. The flame front has plenty of time to travel from the spark plug to the cylinder walls. Between the rapidity of combustion and the spark advance, combustion is completed very early in the expansion stroke, typically by the time the crankshaft has moved ~20 degrees past top-dead-center. This is true even at high RPM because the turbulence created at high RPM increases the speed of the flame front; it’s why a Corvette can idle at 600 RPM and also make power at 6,000 RPM.
As for limited oxygen, modern port-injected automotive engines are designed to bring in enough oxygen to burn the fuel completely, and no more. If you put in less air/O2, you’ll end up with more HC/CO emissions; if you put in more air/O2, you won’t reduce the CO/HC emissions very muc at all, and you’ll also end up with more N2 emissions.
Cars don’t pollute much, owning to the incredible performance of modern emissions control equipment. Catalytic converters reduce NOx/HC/CO levels by a huge amount: tailpipe-out emissions are a fraction of engine-out emissions.
It’s possible that an open-air burner inside a steam engine would produce less raw HC (due to reduced wall-quenching effects) than an IC engine, but entropy still insists that combustion will never reach 100%; you’ll still have some HC and CO in the exhaust, and nitrogen + excess O2 + heat means you will also have NOx. Without aftertreatment, the pollution from a steam engine’s burner will certainly exceed the tailpipe-out emissions from a modern car by a wide margin.
OK, I’m happy to be schooled, that’s why I’m here. Thanks for the information. I admitted to not being an engineer, just a biologist. Next time maybe we’ll discuss a subject on my turf :D.
If steam engines actually do burn at lower temperatures than ICEs, that explains why they fell out of favor. The absolute maximum efficiency of any heat engine depends on the ratio of the temperatures of the hot and cold reservoirs. The cold reservoir is generally the ambient environment, which you can’t do much to change, so maximum possible efficiency increases with an increase in the temperature of combustion. And well-engineered engines usually get pretty close to that thermodynamic maximum.
The problem I see with a steam engine is it takes time before it gets a head of steam up to go and once you park it, it all goes to waste.
If I was in the market for a steam powered car I would expect it to be a hybrid. It would have a rather small steam turbine built who’s job would be to charge the batteries for the electrically powered wheels. This would allow it to operate at it’s best efficiency rather then whatever is the current demand.
It should probably ask the driver if the trip will be longer then 10 minutes to see if it’s worth turning the steam on and you would have to get used to the engine running for a while after you arrive.
A non condensing steam plant will use a lot of water that will have to be carried around.
A condensing steam plant takes a lot of auxiliary equipment. Boiler, condenser, condensate pump, air ejector, oxygen removing preheater, feed pump just to name a few.
Other than trains recip steam engines went out in the 20’s because they were not fuel efficient.
On a direct drive recip train the speed of the train is limited by the diameter of the wheels. Rule of thumb was that a train’s stop speed is limited to the diameter of the drive wheels. 50 inch wheels 50 mph.
A train starts slow because it is heavy and has a lot of mass and it can not start with full power. If it was given full power the wheels would just spin. As the train picks up speed the throttle is opened up. The big boy train had a very high top speed. Big steam engines can develop full power through a wide range of RPMs. Claiming that a transmission would be required and using a trains slow starting as an explinatin is wrong.
A Doble built a hundred years ago could go from stone cold to pulling away in about 40 seconds. They used flash boilers not a big conventional boiler.
Really, every thread we have on this subject follows the same pattern. Someone posts about steam cars (the Doble is the best example) that were actually built and ran extremely well about a century ago.
Then every third or fourth post for about the next page and a half comprises someone saying steam cars would necessarily have problems that Dobles didn’t have, or lack performance that Dobles did have, a century ago.
And it’s not just you, Aquadementia. Take this post:
This is a truly - how shall I put this? - impressive effort, AdamF.
At post #33 I correct **Sailor **by pointing out that the Doble steamer could accelerate from 0-60mph in 15 seconds and had a top speed of 90mph, and that modern stripped down versions can go 0-75mph in 10 seconds and have reached 120mph, and Dobles have no gearbox or clutch. Yet within 12 posts you make exactly the same error again.
There are previous discussions on this topic where I have just given up on the thread in despair over the apparent blind spot people have about it. I can think of few subjects where people insist so blindly on preferring their half baked erroneous engineering theory to empirically proven reality.