I have some questions about series hybrids like the theoretical Chevy Volt. In the typical use case where the driver rarely exceeds 40 miles before returning home and recharging, the engine will be infrequently used. Is it likely to have problems starting when it does finally kick in? Given that most engine wear occurs on startup, do these engines quickly wear out?
Some more hypothetical questions are what type of engine would be best for a series hybrid? Alcohol burning? Gasoline? Diesel? Gas turbine? Can/should the exhaust be used for additional generating capacity (i.e. like a turbocharger that runs a generator instead of a blower)? Would it be better if there were independent electric motors in the wheels instead of one with a drive train transmitting power to the wheels?
Well, given that the majority of engine wear occurs at startup, and that the engines will only start up but rarely, yes, that stands to reason that on a per-start ratio, those engines will wear out sooner: if my car’s engine gave out every 30-40 times I started it, I’d be mightily annoyed, but with the Volt, if you operate it the way you’re supposed to, those 30-40 times might well exceed the life expectancy of the rest of the car…
While this is true, it doesn’t necessarily mean that it’s a horrible amount. Plus it’s really “cold startup” that wears more.
Modern engines don’t need ring jobs as often as the older engines, for example. It’s got to be a really badly mistreated engine, and usually will outlast the rest of the car.
If you’re using the car in such a way that “the engine will be infrequently used,” then it’s not starting very often, either. I presume (although I don’t really know) that once the Volt kicks the engine in, it will keep the engine on for a reasonable length of time, so it’s likely to have fewer starts than a normal engine.
In any case, the manufacturer could add some additional hardware to mitigate startup issues if these were anticipated to be a problem. Whether or not the Volt has these, I don’t know. Whether that’s helpful depends on whether you’re asking a theoretical question or one based on the Volt specifically. (And, as stated above, “cold” and “warm” startup are different things, in any case.)
You could use any engine you desire. What engine is “best” depends on what you’re optimizing for.
One interesting aspect of choosing an engine for a series hybrid is that the engine power output is disassociated from the instantaneous power required at the wheels. That means that the engine doesn’t have to perform effeciently (or at all) over a range of speeds and loads; it just needs to produce power at a handful of predefined points. That means you can consider engines that may not be suitable for a traditional automobile.
On the other hand, the engine is hooked to some kind of power transfer device (a generator, in the case of the Volt), so you have to consider matching gererator and engine performance–it does no good to have a great-performing engine if it only runs at points where the generator performs poorly.
All this is a long-winded way of saying, “it depends.” You can’t really point to a specific engine and say, “that engine performs best in a series hybrid” without taking a lot of other things into account.
Sure, what the Hell. Why not? Or, really: if you can do anything to make the power generation more efficient in a cost-effective manner, why wouldn’t you? Question is, of course, a) can you create a device that would increase overall efficiency, and b) how much does it cost?
Part count would drive you to using a single motor rather than multiples–fewer parts are, in general, cheaper.
Sure, but then you get backpressure on the engine cylinder exhaust, which lowers the efficiency of the engine. I suspect it would not be worth it, given that few current gasoline or diesel engines use turbochargers for efficiency.
I hope sweeteviljesus doesn’t mind if I piggyback a question… I’ve read that the Volt can travel up to 400 miles to recharge the battery, I believe. What happens after that 400 miles? Can you just fill it up with more gas and drive it as normal, or does the battery kick in again once it is recharged?
It sounds like a neat car - hopefully it will work well and not have too high a premium.
When the battery runs low, the engine kicks in to recharge the battery. You can continue to drive if you refill the tank. I don’t know how far you can with the engine charging the battery.
Consider the following scenario: I drive my Volt to and from work for a total round trip of 25 miles and then I recharge overnight. On long trips, we take my wife’s car, so that over the course of a year, the gas engine (or diesel or whatever) never kicks in. Then one day, I need to go on a long road trip. What issues might I encounter with the gas engine, assuming it wasn’t a lemon? Of course, if it were a lemon, I might not know it for a whole year.
I was unaware that generators were optimized for certain input speeds, but couldn’t any engine type be optimized to match the generator?
As far as part count is concerned, with independent motors, you eliminate drive shafts, u-joints, transmissions (although I am not sure an electric motor needs one), differentials, etc. It seems like a drive train means a higher part count.
To hijack my own thread a little, can regenerative breaks wear out? Are they just simple Faraday generators or is there a friction component like in a traditional break. I would expect that there is some sort of mechanical emergency break, but like the name says, I would expect that that is for emergency use only.