[OilBurner]

That's an interesting point about driivng style, I know for certain that if most people drove more smoothly, progressively and at sensible speeds they would see a big increase in their fuel economy returns anyway.
That you have to do that for the Prius shows that in the hands of a regular impatient and inefficient driver, the returns will be disappointing. My regular 2.0 Turbo diesel can return 60mpg + (imperial) with very careful driving and overinflated tyres. In normal driving you'd get around 50mpg without being too careful. I can get a routine 57mpg even whilst driving in a hilly area (the Highlands of Scotland) and flooring the throttle regularly to overtake slower traffic. That's with me, my wife, our 30kg dog and some luggage aboard. Also, I play CDs constantly and use the air-con a lot. Not bad eh?
So I still contest, petrol hybrids are no great step forward.
So we come full circle, you can get good returns in a diesel car but hybrids require better driving skills to make the most of them - therefore they're not as good as they might appear on paper.

What I would really like to see is the Prius stripped of it's electric motor, regenerative braking etc and just left with the 1.5 petrol unit. What economy could that car acheive then? I'm willing to bet that the reduced weight by removing all that extra hardware would bring the economy up to a similar level to the off-the-shelf hybrid version.

BTW Devil, did you have any particular reason why diesels couldn't be used with hybrid technology?

[Devil]

Diesels don't like start/stop use. The mechanical strain on its components is much higher than with a petrol engine (which is why, size for size, they are already heavier). If a diesel engine were to be built for this, with a reasonable lifetime, it would weigh much more (higher consumption) and cost a small fortune. Furthermore, running a diesel intermittently in Arctic conditions could create a fuel-freezing problem in the pipes, with the car running electric. I'm not saying this could not be overcome, but it would mean another pump to consume electricity. A third point is that the injection during starting is rich (hence the traditional black cloud for a second while starting a diesel), so that the regular stop/start would be more polluting.

I very much disagree with your idea of stripping the hybrid out of a hybrid. It would not work. Let's assume you have a 100 HP @ 5,500 rpm engine in a hypothetical conventional car. It runs inefficiently because the speed varies under load from, say, 1500 to 6000 rpm and idles at 800 rpm, while it generates max torque at 3,500 rpm. This involves much compromise. Then, on a time-weighted average, you generate only 30 HP, perhaps using the 100 HP once a fortnight, when you have to accelerate out of trouble. The idea of a hybrid is that you have a much more efficient engine with a very limited rpm range generating, say 40-50 HP and a relatively low torque. This provides all the energy you require, and some, so it can be switched off (no wastage during idling) when no more energy is required (battery fully charged). But a high torque is required for accelerating from standstill, and such an engine could not do it, so this is where the electric motor kicks in, as it is a relatively high torque-low power device. The two power sources therefore complement each other. I can assure you that if you coupled such a petrol engine mechanically to the wheels as a sole power source - remembering this is a mid-sized car which would normally merit a 2.5 l engine - you would need a 12-speed gearbox and a lot of skill to drive it and, even then, you would drive constantly with your foot hard down on the accelerator pedal -- and it still wouldn't pull the skin off a rice pudding.

[OilBurner]

I'm sorry Devil but your idea that the Prius is too big to be driven with a "mere" 1.5L engine doesn't add up.
The Prius is 4450mm long, 1725mm wide and 1490mm high. The Toyota Corrola Verso is 4360mm long, 1770mm long and 1620mm high and "makes do" with a 1.6L 108bhp engine and manages 0-60 is a OK time of 12.6 seconds and 38mpg combined. Hardly too slow or uneconomical for a car with a poorer Cd than the Prius and offers seating for 7. The regular Corrola with a 1.4L engine does over 42mpg - I reckon the Prius would do about 50mpg if stripped out and fitted with the same engine.
Not that long ago Ford offered the Mondeo with a mere 90bhp 1.6L engine and that car went, although not too quickly. 2.5L in a Prius sized car is complete overkill.

OK, the standard 1.5L Prius unit may not work too well on it's own because it was designed to use the electic back-up, but put a standard Toyota 1.4 or 1.6 L unit in and it would be just fine.

I think you've missed my point: the Prius has a lot of extra hardware weighing it down that affects economy, strip that out and you'd find a big improvement that would counterbalance the loss of electrical assistance from regenerative braking.

I take your point about the mechanical strain on diesels though - that could be an issue. However, the black smoke on start-up is practically history on common-rail units, especially when they're warmed up.

[kenbathrhume]

The Prius engine is a little different than other engines though.

It is 1.5L but only 70hp. It uses the ATkinson cycle, which has a longer power than compression stroke. This is inherently more efficient but gets much less torque and hp.

What you'd basically want if you want to get rid of the hybrid stuff in the Prius is those cars you mentioned. They'd get about 40mpg (US). I think Toyota has variable valve timing. I would guess this would make it an Otto cycle (more hp less efficient) at low rpm while accelerating and more of an Atkinson cycle (more efficient) at constant speed.

That is fine, but the hybrid's sole reason for being is to get better gas mileage and possibly less wear on engine so it wouldn't make sense. If you want a dehybridized Prius, you can buy a Corolla.

[smiley]

Still I would prefer this car.

http://www.rsportscars.com/eng/cars/speedster_eco.asp

During initial testing the 112 hp concept car reached a maximum speed of more than 155 mph while fuel consumption on the combined cycle was an incredible 113 mpg.

[RegGuheert]

Neat car, Smiley!

For the record, my 27-month-old Honda Civic Hybrid with 21,000 miles has achieved a lifetime average mileage of 48.0 mpg (US gallons). That's precisely what's on the EPA sticker.

I've read a couple of the reports from the car enthusiast magazines of low hybrid mileage and my conclusion is that those articles are written by lead-footed individuals. IMO, the target market for those magazines are not people trying to save the planet, but rather people who enjoy driving cars...

I will say that my Civic Hybrid got mileage in the low 30's once when I drove it up to Ottowa, Canada in the middle of winter. The car really got much worse poor mileage in the cold climate. I think the fuel mixture used up there was part of the issue. I've often wondered how much a normal car is affected by the cold temperatures.

Finally, while diesels may have improved their emissions, when comparing production cars currently sold in the U.S., diesels tend to have the worst emissions while hybrids have the best. The mileage reported for the production diesels is pretty good, but lower than the hybrids:

http://www.epa.gov/greenvehicles/smcar-04.htm
http://www.epa.gov/greenvehicles/midcar-04.htm

Thoughts?

Reg

[OilBurner]

The problem with reported figures, as you rightly point out, is it depends on the driving style.
Lead-footed journalists are probably read by lead-footed drivers too. So it's representative in my book.

Interesting quote from this weeks AutoExpress. They're long-term testing a Prius.

More recently though, we've thrown some longer journeys at the Prius and the fuel economy has come tumbling down - over the past eight tanks we've managed 45.6mpg. If this is maintained, the model will be no more economical than a regular turbo-diesel hatchback

They were getting about 68mpg (imperial) whilst doing mostly town driving.

So in all fairness, a hybrid may be very good if you happen to drive it on roads that suit it, otherwise it'll do little better than a regular diesel car.

[OilBurner]

p.s. fuel economy tends to be worse in winter due to the cold starts that means the engine takes longer to get to it's ideal operating tempreture where economy is best.

[smiley]

p.s. fuel economy tends to be worse in winter due to the cold starts that means the engine takes longer to get to it's ideal operating tempreture where economy is best.

Another problem is the tyre pressure, which decreases. This also has a strong impact on the fuel economy.

[Devil]

I will say that my Civic Hybrid got mileage in the low 30's once when I drove it up to Ottowa, Canada in the middle of winter. The car really got much worse poor mileage in the cold climate. I think the fuel mixture used up there was part of the issue. I've often wondered how much a normal car is affected by the cold temperatures.

I don't know about your car, but I believe some hybrids have a problem with heating/cooling where the passengers sit. Let's just reflect a little.

A conventional car uses hot water from the cooling system for heating and a compressor turned by the engine for cooling.

A hybrid can't use hot water conveniently because they have to do their darnedest to keep the engine as hot as possible for economical starting at more or less frequent intervals, perhaps every 20 or 30 minutes in some conditions. If you pump freezing cold air through a heat exchanger in the coolant circuit, you lose the necessary heat.

A hybrid can't use the engine to turn the compressor either (which is inefficient, anyway), coz the engine ain't turning when you're stuck in that tailback, and it's 40°C outside.

So what can you do? The same as in your home, you can plug your aircon (reversible heat or coolth) into the power socket. But aircons take a lot of energy, especially if they are used at -20°C for heating or +40°C for cooling, so its draining your battery flat in next to no time. Ergo, your petrol consumption shoots up like gangbusters. 'Tis the price of comfort.

[Devil]

If I could edit (Grrrrrrrrrrrrrrr! I can't ) I would have added this as an afterthought. Have you ever driven a small car (say 1.5 to 1.8 l) with aircon on? Every time the aircon kicks in, the car slows noticeably and vice versa. On climbing long, steep hills, the makers even recommend you turn the aircon off. It takes that much power out of what's available for driving the wheels.

[OilBurner]

It's very true about the effect of air-con on "smaller" engines. On my 2.0 diesel you can hardly tell, even on steep inclines. My wifes 1.6 petrol slows down to the point where you have to turn the a/c off if you want to pull off quickly in traffic!!

Do hybrids suffer equally badly with the air-con on, I wonder?
It sounds like they suffer quite badly when trying to heat the car.
Presumably hybrids use heater elements rather than the cooling system to generate cabin heat?
That must be quite wasteful as a regular cra gives off that heat pretty much for free!

So far then, the anacdotal evidence suggests that hybrids are great unless you drive lots on open roads, use the air-con or the heating. I think my original claim that there's more hype than genuine benefits looks stronger all the time.

[Devil]

It's very true about the effect of air-con on "smaller" engines. On my 2.0 diesel you can hardly tell, even on steep inclines. My wifes 1.6 petrol slows down to the point where you have to turn the a/c off if you want to pull off quickly in traffic!!

Do hybrids suffer equally badly with the air-con on, I wonder?
It sounds like they suffer quite badly when trying to heat the car.
Presumably hybrids use heater elements rather than the cooling system to generate cabin heat?
That must be quite wasteful as a regular cra gives off that heat pretty much for free!

So far then, the anacdotal evidence suggests that hybrids are great unless you drive lots on open roads, use the air-con or the heating. I think my original claim that there's more hype than genuine benefits looks stronger all the time.

Of course they don't use heater elements. They use the aircon in reverse, just like a household split unit. No added components/weight and with a heating efficiency of about 250% (joules out x 100/joules in), whereas heating elements are about 95%. Of course its not wasteful. And I might add that your wife's car probably consumes 1.5 l/100 km more when the aircon is on.

Furthermore, there is no such thing as a free lunch. Nor is there free heat in a conventional car. The heat you use in winter is there because the fuel efficiency of the engine is abysmally low and the joules come from the petrol you put in the tank. You therefore pay for that heat at an exorbitant rate, most of which goes to the government. The engine in a hybrid, being more efficient, generates less heat for a given fuel consumption therefore there is no heat to spare for heating the car: it is all kept to keep the engine warm.

The hype is probably in your personal convictions.

[OilBurner]

I disagree, the heat in a conventional car is coming straight off the cooling system. Yes, it takes heat away from the engine, but much of the heat would have been lost anyway - turning on the heat for the interior only has a slight cooling effect.
Whereas in the hybrid, you need to turn the air-con on to either cool or heat the car. The compressor must use a fair amount of power to drain performance like they do. Probably about 5hp-10hp I'd guess.
Surely that's less efficent than just using the heat that a regular car would otherwise lose to the radiator?

I agree on the whole though - the Atkinson cycle is more efficient so your overall economy should always be better when comparing cars driven in the same way using the same features. Providing of course, you're comparing two petrol motors.

The hype is probably in your personal convictions.

You may be right - but I'm concerned with the increasing reports (anecdotal though they maybe) that hybrids are not delivering everything they promise.
I'm a self-confessed petrolhead (car nut that is) and have no interest in seeing the demise of the motor car.
I would be genuinely pleased if the hybrid really was a revoultion in motoring. I'm just not convinced it is yet.

[kenbathrhume]

A home air conditioner is how many watts would you say? A 5000 BTU air conditioner would I assume use 5000BTU per hour, that's about 1.5 kwh /hour (1500 watts) or approx. 2 horsepower.

That's for a 5000 BTU in your house, how much would you need for your car? 1/10 that?

Most of the time when you are on the highway, you're only using 20hp or so on the wheels. Engines are much bigger than this b/c of the need to accelerate.

So if an air conditioner was 30% efficient (energy in gas to energy in cooling use - same as the overall car) then that is 450 watts which means it's using about .015 gallons per hour.

My numbers may be off somewhere, that doesn't sound like much.

[OilBurner]

It still makes a big difference to economy, whichever way you look at it.
And the difference it makes during acceleration indicates to me that it's quite a big drain - I have to admit, I don't know exactly how much though!

[OilBurner]

I found this article:
http://autorepair.about.com/cs/generalinfo/a/aa062300a.htm

It claims a/c uses around 8hp. That does sound a lot. Maybe there is a reason why a/c in cars is less efficient?
That certainly tallies with my intuitive feel for how much power is drained from having driven several dozen cars equipped with a/c.

What I need now is a figure for how much of a drain using the regular heater is..

[Andy]

A small home AC unit uses more than 1.5 KW per hour if run continuously. I would guess a figure of 4 KW is more appropriate. I think using the AC in a car consumes nominally about 5 - 10% of the power output depending on AC compressor size and the climate the car is operated in.

Heat in winter from regular cars is essentially a free commodity. About 30% of the energy in a gallon of gas is dissipated through the radiator with another 30 - 40 % dissipated out the tailpipe. No extra fuel is burned to heat a car. It would be very good if they could develop small automotive absorption units using waste heat for cooling instead of compressor driven systems.

With regards to the argument that current hybrids are overhyped, I agree . The nominal energy efficiency increase seems to be about 40 - 50 %. A simple diesel car can achieve most of that increase 30% or so without all the complexity and will last longer all things being equal than the hybrid. A diesel hybrid can achieve all the benefits of current hybrids in additition to having more longevity and being even more efficient. I don't know of any gasoline engine (Atkinson Cycle included) that can achieve the 44% or so peak thermal efficiency of current automotive diesels. It will probably cost an extra $1,000 - $2,000 but will last longer thus covering the higher energy penalty of manufacture.

Diesel emissions with the use of particulate filters and urea/ammonia NOX systems and zero/low sulphur fuel should achieve the similar emissions performance to present gasoline engines, in fact probably beating them on HC and CO emissions and definitely on CO2 emissions.

[Devil]

You haven't caught on to what I said.

A good aircon is about 250% efficient, whether it is heating or cooling. Yes! 250%! Why, because it is a heat pump. It extracts heat from one source, through a heat exchanger and dissipates that heat through a second exchanger. The medium to transfer the heat from one to the other is a refrigeration fluid (in cars, usually an HFC).which uses the latent heats of vapourisation and condensation under pressure, with the release of the condensed liquid through an expansion valve to generate the coolth. It does not generate heat, it simply transfers the heat from one exchanger to the other. It can therefore be used equally well for heating or cooling.

The compressor in a conventional car is highly inefficient because it has to work with crankshaft speeds of ~800 to ~6000 rpm (through a pulley/belt reduction). If it works while idling, then all the extra energy put into it at full revs is simply wasted. Therefore it wastes a considerable amount of fuel, witnessed by consumption rates rising by typically 1-1.5 l/100 km when you switch the aircon on (perhaps less with larger engines, because they are run at lower crankshaft speeds for longer times).

An electric-driven compressor, which runs at constant speed, is much more efficient, because the motor speed is optimised for that one job. Notwithstanding, the passenger compartment of a car is sheer hell to heat or to cool. In summer, you have vast areas of glass (even IR-reflective) letting in radiation. Round that, you have a thin steel shell covered by a heat-absorbent film of paint and dust/dirt, with microscratches over the whole surface, with almost no insulation, just the trim on the inside. Why does a dog or a baby shut inside a car die within 30 minutes if it is parked in a hot sun with the windows closed? Because the joules entering are ginormous and the aircon has the job of keeping all that heat down to a reasonable level, by pushing those joules to the hot exhanger. In fact, the heat input to the passenger compartment of an average car on a hot summer's day, in the sun, is between 3 and 5 kW.

Conversely, the heat lost when heating a car in the Canadian winter requires more than 5 kW to replace (not many cars have double glazing, do they?).

So let's say, for convenience, we need 5 kW in or out under peak conditions. As I say, a heat pump of the type suitable for this application is 250% efficient, so it requires 2 kW of mechanical energy to turn the compressor, or 2.1 kW of electrical energy. So, under extreme conditions, yes, this is a hefty load on the battery of a hybrid car. But under most normal conditions between Churchill and Phoenix in N. America or between Lulla and the Med in Europe, the duty cycle of the aircon will be much lower than under these extreme conditions (even at 40°C driving in full midday sun, the aircon on my car kicks in for only about 60% of the time to keep the compartment comfortable).

As for home aircon units, I have 1 18,000 BTU (yes, we have not gone metric there!!! ) unit, 2 12,000 BTU and 3 9,000 BTU units in my house. I have studied only the 12,000 BTU units for consumption. The starting surge (at 230 V) is enormous, about 12 A or 2.75 kW, lasting for about 1 second. After that, when it is actually running, it consumes about 1.2 kW but, with a duty cycle of about 65% in hot weather, it averages only about 800 W when on. The real problem with aircon is that they are misused. At the moment, it is just after 11.00 and the temp outside is about 38°C. I am in a small room (~15 m2) with two computers and their peripheries running. This room has a 9,000 BTU unit but it is not switched on. Why? because I'm reasonably comfortable without it. The SE-facing window is shuttered, double-glazed with IR coating. The walls are 16 cm air-channelled bricks. I anticipate I'll need to switch on the aircon for about one hour, this afternoon, when it will probably be ~41-42°C. It is set for 28°C, which is very comfortable for the dry heat we have here. So, to keep this computer room comfortable for my working day, I possibly consume about 500 or 600 Wh of juice. For the whole house, it is doubtful whether we consume more than 1.5 to 1.8 kWh/day under these conditions (exception when my wife is ironing the weekly wash, when she runs the kitchen aircon for about 3 hours). Our neighbour, in a similar house, has 5 split level units on 24/7, set at 20°C, which I consider stupid and energy-profligate - and must make it sheer hell when he goes outside.

I mention this to illustrate that it is easier to remain comfortable in a house than in a car, the latter requiring MORE energy to do so.

[OilBurner]

Thanks Andy, I think that neatly clarifies what I was trying (and failing) to say!! :D