What ever happened to series hybrids?

Turbines are not very efficient unless they run at full power. Since the power required by a car varies a lot, making good use of a turbine requires a big battery for storing surplus power when the car's power demand is low ("load levelling").

Meanwhile, Toyota invented HSD, which makes excellent use of an internal combustion engine without using a very large battery. And now plug-in hybrids are on the horizon...

 

Series-hybrids will make their big comeback when the batteries in PHEVs get bigger. About 70kW electrical output and 30 mile EV range, people will start thinking about switching to serial. But as Richard said, Toyota are continuing with a parallel arrangement for now while the Prius makes do with a small battery.

 

<div class='quotetop'>QUOTE(clett @ Aug 14 2006, 12:54 PM) [snapback]303159[/snapback]</div>

Actually the Prius is a hybrid-hybrid in that it is a series hybrid at low speeds or high load situations such as hill climbing and a parallel hybrid at crusing speeds.

The amount of power transferred through MG1 to MG2 relative to the power transferred directly varies depending on the instantaneous power requirements.

Pure series hybrids require large motors and generators and suffer form the inefficiency of conversion - e.g. the motor/generators on Prius are about 90% efficient but put the two in series and you only get about 80% out of what you put in. the mechanical path is about 95% efficient so you get about 15% better economy at freeway speeds with the HSD than with a pure series hybrid.

kevin

 

<div class='quotetop'>QUOTE(marjam @ Aug 14 2006, 12:38 PM) [snapback]303027[/snapback]</div>

http://en.wikipedia.org/wiki/General_Motor...1_Series_Hybrid

60-100mpg

In the end I would rather have a plug in Prius even with less range, the EV1 has far less usable space then the Prius.

 

<div class='quotetop'>QUOTE(richard schumacher @ Aug 14 2006, 02:56 PM) [snapback]303126[/snapback]</div>

WRONG

your thinking of maximum efficiency. and they are actually efficient elsewhere to. Ever notice the top speed of an aircraft and its cruising speed aren't the same thing?

it would probably be more efficient but turbines have serious draw backs. this was tried on semis in the 60-70 by international I believe. perfect usage right? long long periods of steady state cruising (just like a flight to tokyo) but they are very very precise to build and very expensive to maintain/fix. and while the motor/generator in the prius may be whatever efficient the loses in the drivetrain are more significant than quoted..and if an ICE operated at 90% efficiency you would be able to grab the exhaust while its running

 

The peak thermal efficiency from a small turbine is too low - only about 25%.

This is because they suffer from heat loss and poor compression ratio. An ICE is able to achieve a much better compression ratio because the combustion area is sealed. There is no seal in a turbine, so only big (like powerplant) turbines can get reasonable compression ratio and hence up to 40% efficiency.

By comparison....

A typical gasoline ICE gets about 25% efficiency. (10:1 expansion ratio)
Prius "Atkinson" cycle ICE gets about 34% efficiency. (13:1 expansion ratio)
VW diesel engine ICE gets about 43% efficiency. (20:1 expansion ratio)

So in terms of thermal efficiency, a diesel engine is by far the best way to go.

There are some good 600 cc diesel units from Japan that, with some serious forced induction, could give say 80hp or so. This would be a tiny, light-weight unit with very high efficiency and more than enough power for a series-hybrid. Not much in the way of raw materials, so cheap too.

 

Seems to me like diesel prius would be the way to go, at least for Europe where smog isn't such a big deal. I'm also guessing that the puff of smoke you see in some of the more powerful units is due to turbo lag (extra fuel goes in via the accelerator, but not enough air), so perhaps this could be cut down with an engine changing speed less rapidly (as could be managed with HSD). Or how about a supercharger, or electric turbo?

Then again, how about an Atkinson/Diesel engine? Is there a reason why this wouldn't work?

I had a great idea for a steam driven car that used mechanical heating of water to reclaim energy under braking. Go on, ask me about it

 

<div class='quotetop'>QUOTE(clett @ Aug 16 2006, 06:33 AM) [snapback]303970[/snapback]</div>

Hi Clett,

Thanks for all the electric battery stuff you have put on here and priusonline.

I am wondering what a electrically compounded turbo Atkinson engine would do? That is using a turbo on the exhaust to generate electricity for the drive battery. Might be some technical problems with magnets an high temps, but maybe not with the high expansion ratio engines. Have you run across any info on this?

 

Thanks; I should have written that turbines are not very efficient over a wide range of power outputs.

 

<div class='quotetop'>QUOTE(clett @ Aug 16 2006, 05:33 AM) [snapback]303970[/snapback]</div>

You might want to recheck your thermo. Modern bypass fan turbojets are in the range of 60% efficient. There is also a group of small scale turbines on the horizon in the theoretical range of 70+% using some really nice triple spool designs. Compression ratio is not a function of seal in the turbine and you seem to be basing your thought process on static CR which is a completely useless measure in the minds of almost all proffesional motor builders

why add yet ANOTHER system to heat water off the brakes? just reverse the damn electric motor

 

You can mechanically heat water, it can be apparently extremely efficient, like 90-something percent. So you could have a tiny gasoline burner that heated water (wonder how efficient this could be? A normal burner has to let hot air escape out of the chimney, to keep fresh air coming in, but you could aspirate it some other way...) and instead of regen breaking you could use a clutch to bring in mechanical water heating to pre-heat the water. You could recycle the water, but not re-use the heat that you got back, because otherwise the heat wouldn't be going anywhere and you'd not be able to do any work...

Anyone got the low-down on modern steam engines?

 

Not exactly sure. It needs someone to come up with a very efficient boiler of some kind. According to my dad who used to do the calculation in his lessons, boiling water in an electric kettle is something like 98% efficient. How efficient are steam engines? Might be able to come up with something that was more efficient than an electric motor if you used a battery to boil water!

 

<div class='quotetop'>QUOTE(molgrips @ Aug 22 2006, 09:52 AM) [snapback]307497[/snapback]</div>

RE the turbine engine: Actually, it was Chrysler who built 50 experimental cars (as 1965 or 66 models, I believe) and allowed 'average' (ie white, upper-middle class) Americans of the era to drive them for a period of months.

The cars ran well and even had comparable fuel economy and acceleration to ICE powered cars of the era, but emissions concerns were just beginning to take hold; I believe this is what contributed to the demise of the turbine program. Manufacturing concerns aside (and there were indeed many), from what I remember reading, the turbine simply could not be tuned to even get close to the CO standards of the day.

Another problem was the volume of the exhaust stream. The exhaust chambers in the Chrysler turbine car were immense, relative to the pipes in a ICE powered car, and posed a serious packagaing problem. The temperature, at anything above idle, was also too high to be comfortably near pedestrians.

One more thing: it idled at 22,000 rpm (!) This, to me, seems the very antithesis of what the Prius is about.

I think the engineers of the day were envisioning super-powered cars zooming along computer controlled highways at triple digit speeds...not the realities of driving in today's world.

Besides, don't turbines - even today's - take a few seconds to spool up? How could one be started and stopped quickly, as the Prius does now with its ICE...or am I missing something?

 

<div class='quotetop'>QUOTE(molgrips @ Aug 22 2006, 07:52 AM) [snapback]307497[/snapback]</div>

The boiler is not the problem - any heat engine is limited in its efficiency that is determined by its temperature differentials. Any practical steam engine is going to be limited to a few percent efficiency - similar to a railroad locomotive.

Electrical regeneration as in the Prius is not limited by physics in its efficiency - only in its implementation. The motors in the Prius are about 90% efficient and the whole cycle from mechanical->electrical->chemical->electrical-> mechanical is about 50% efficient under good conditions.

kevin

 

If you have the cash, you have a turbine motorcycle now.
http://www.marineturbine.com/motorsports.asp

I was under the impression that the fact they couldn't put a catalytic converter on it was Chrysler's problem with the car in terms of meeting the new emission regs. Not necessarily that it couldn't be made clean. One of the racing federations also had banned turbine engines at the time. Which eliminated an avenue for R&D with it.

 

Hi All,

I actually saw one of those Chrysler turbine cars when I was a kid. Was not too obnoxious. Idling was pretty quiet actually. Something like a big heavy Delta Unisaw Table saw, with the blade about half way up, and not cutting wood. But, there were not any dog's around either. At 22 K RPM, the dogs might have had an issue with the car.

Yea, there was a Turbine Indy racer - Granatelli was the name of the guy who raced it. It was pretty impressive. When they banned turbines in American racing after it did well. That was a big turn-off for me as a kid. Never thought of pursuing any kind of mechancal carreer after that.

I read up later on about the Chrysler turbine automotive engine. In the last incarnations of the engine they implimented a rotary ceramic regenerator, to cut down on exhaust temps, and improve fuel economy. They never reached V8 fuel economy because of gearing losses. Which is why series Hybrids with turbine prime-movers have been of interest. With shotky-barreir rectifiers, its possible to have high efficiency high speed alternators, and acheive high drive system efficiency for a road car with a Turbine engine. Also, there is synergy, as the Turbine would not need to be as big in a hybrid car, and thus the cost of manuafacture might be OK. Rather than machining the blades, there was talk of various powder metal methods that have come along since the 60s, or even CERMET blades (or impeller), that are made like potery, but have metal impregnated into a porcelan matrix for tuffness.

Yea, that Crysler turbine engine was about the same size as a V8. So, it had lots of power.

Modern high efficiency power company turbines use regeneration, and reburn (injecting fuel into a second set of combustion chambers, as there is still plenty of oxygen) to get up to the 40 to 45 % efficiencies. I doubt these technigues could be replicated in a pratical automotive turbine package. There are also issues of Reynold's number. The diameter of a turbine has to be relatively big for the air-flow to have lower drag. In discussing air-ducting for dust collection, 6 inches is really a practical lower limit for a professionally effective diameter. This is a very very powerful turbine size - maybe like 500 to 1000 HP!?

Aircraft turbines achieve high efficiency by getting a higher effective compression ratio at cruise, due to ram-air compression. The Concord infact, did not have enough range to cross the Atlantic sub-sonic due to this. Only at super-sonic speeds were the engines efficient enough to make it across, even though the supersonic speeds had dramatically more drag. The effective compression ratio at supersonic flight was like 60:1 ! Versus 10:1 at 0 speed.

External combustion is usually less efficient as the max temperature is somewhat less. This is because the max temperature limit is set by material science. The hot gases have to be piped to the expander (piston, turbine, whatever). The pipes melt. Combustion gases touching the cooler metal tend to genrate CO , and incomplete burn. In an internal combustion engine the full heat of combusted gases really do not make full contact with the engine parts, alowing hotter temperatures in the fireball of combustion. By the time the gasses expand, they have transmitted work to the mechainical engine parts by pushing on the cooler gasses near the mechanical parts, and thus have cooled as well. This allows a hotter peak temperature with economic materials. When is the last time you heard of a steam turbine with Aluminum blades? This is what makes turbines expensive, as piston engines almost all use aluminum alloy pistons (some with oil-spray cooling from underneath). Its very difficult to cool the blades in a turbine, so the materials just have to take the abuse. Besides being more expensive materials, the blades are very complex shapes cut into those hard to machine metals.