Submitted by Live_Strongerrr t3_10o8vih in explainlikeimfive
hikingsticks t1_j6d7l32 wrote
Reply to comment by [deleted] in Eli5 why aren't gas only vehicles far more fuel efficient than before by Live_Strongerrr
I think the most recent production ICE engines are tending towards 45% efficiency, which is incredibly impressive.
Also people expect more gadgets these days - heated seats, steering wheels, computers and screens, AC in winter for dehumidification, and so on. All of these put more of a load on the engine.
sault18 t1_j6dc1vp wrote
Those high efficiency numbers are in lab conditions at ideal operating parameters. A lot of these high efficiency numbers come from test engines that are years away from being in use or are so exotic that they will never be used in a production car.
In the real world, car engines hardly ever operate at their maximum efficiency point. Add in idling, engine warm up time and the inability of conventional gas cars to recapture energy from regenerative braking and the actual efficiency is much lower.
hikingsticks t1_j6doxp3 wrote
Of course, yes. But those same factors affected older cars as well. Peak efficiency in lab engines is higher now than it was 20+ years ago, and efficiency in terms of real life use is also higher now than it was 20 years ago.
Hybrids start to bridge the gap with regenerative braking, but then of course its not purely an ICE vehicle anymore. Technically if its not a plug-in hybrid then all of the energy used came from the ICE, so you could argue that its an ICE vehicle with additional efficiency technology installed. That addition alone significantly improves the efficiency in terms of miles per gallon (or equivalent metric), but doesn't alter the thermal efficiency of the engine itself.
sault18 t1_j6dscmt wrote
>but doesn't alter the thermal efficiency of the engine itself
Slight correction. Hybrids like the Prius use a slightly different engine cycle than pure ICE cars. Basically, the intake valve closes later in the Prius engine so the engine doesn't compress as much air as if it intake valve closed right after the intake stroke finishes. This means the expansion ratio is greater than the compression ratio, trading power for efficiency. The addition of 2 electric Motors helps make up for some of the loss in power. The electric Motors/ generators also allow the car to control the gas engine speed and not rely on the throttle so much to do so. This allows the car to run with the throttle more open and even wide open a lot more of the time. This reduces the pumping losses since the engine is not sucking air through a restricted throttle a lot of the time. To top things off, this also reduces pressure drop that would normally happen across the throttle in a conventional ICE car, increasing the air available in the cylinder.
hikingsticks t1_j6dvtfd wrote
That's a good point about allowing the engine to run closer to peak efficiency more of the time, rather than having to do exactly what the driver requires. The buses in London are all hybrid diesels, and you hear them pull away from each stop on the electric motors, then the engine starts up shortly afterwards and trundles away as needed. So they can avoid the need for peak power on acceleration which tends to be more inefficient. It probably leads to increased reliability as well.
Regarding the valve timing, from memory that's called the Atkinson cycle. It's also used on non hybrid setups sometimes. I used to have a Peugeot 307 2.0 petrol engine that ran exactly like that, and I've encountered it in a lot of other engines as well over the years. As you said it's a reduction in maximum power output in order to increase efficiency.
sault18 t1_j6dysos wrote
Yeah, the ability to accelerate from a stop up to 5 to 10mph on electric only really boosts city fuel economy. For a conventional car or bus, this is where they have the absolute worst fuel economy gulping down fuel in 1st or 2nd gear. I'd also suspect that bus drivers taking off from a stop in a regular diesel bus would step on the throttle and cause the engine to run a rich fuel / air mixture. So the benefits accrue here as well in the fuel efficiency and maintenance departments.
Going forward, I'm glad we're seeing explosive growth in all electric buses and cars. They're vastly more efficient and simpler than a hybrid drive train, avoiding the tradeoffs between power and efficiency hybrids had to make. Hybridization was a great technology for its time but it's increasingly being supplanted by full electric architecture.
SkateIL t1_j6d8tue wrote
Headlights on all the time.
hikingsticks t1_j6do4ra wrote
Yep, absolutely. Air compressors for air suspension can take a fair amount of power, heated windscreens, the list goes on.
[deleted] t1_j6d8qsk wrote
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Rev_Creflo_Baller t1_j6d9fut wrote
Of course it does. That's what the alternator is for. That plus keeping the battery charged up.
[deleted] t1_j6d9k5t wrote
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redline83 t1_j6dac3i wrote
Only for a relatively short time until your battery is dead. The 12V system while the engine is running is supplied by the alternator, the battery just buffers it.
As proof, you can jump a car without a battery and the electronics will all work.
UglySuperhero t1_j6d9wla wrote
When the car is off the power comes from the battery. The batt gets charged by the alternator when the engine is running.
ArmedWithSponge t1_j6dauj4 wrote
No offense, but you should just google “what powers the radio in my car?” r/Rev_Creflo_Baller is right, it’s the alternator (when the cars on) and battery (when the cars off). Guess what powers the battery and alternator?
trootaste t1_j6dbd54 wrote
Lol I'm not arguing, I understand that. It's not plugged into mains so it has to be the engine, I'm just asking how.
LittleKittyLove t1_j6da9l0 wrote
Because you have a small charged battery which is used to start the car.
Run the radio for a while without starting the car, and your battery dies, and needs to be jump started.
SilverHawk7 t1_j6davvg wrote
Because your car has a battery. The battery can provide power to the lights, accessories, but most importantly the starter, which is used to crank and start the engine. If you leave those accessories on while the engine is off, it will drain the battery (we're talking leaving these things on for hours without running the engine). Drain the battery enough and it won't have enough power to start the engine.
Your car also has an alternator, which is basically just a small generator turned by the engine. The alternator turns some of the engine's power into electricity to power various parts of the engine as well as the lights and accessories, while also recharging the battery.
vector2point0 t1_j6e1r1r wrote
The car has a battery that will run the accessories and be charged by the alternator when the engine is running.
UglySuperhero t1_j6d9lye wrote
Yep. The engine powers the alternator which generates electricity needed for the rest of the car.
someone76543 t1_j6dav2s wrote
The ICE does power all the electronics.
All car engines have a generator ("alternator") attached, which generates the electricity that the car needs. Taking power from that generator puts a drag on the engine's shaft, requiring more fuel to be burnt to keep the car going at the same speed. There is no such thing as free energy, it has to come from somewhere.
There is also a rechargeable battery in the car, used when the engine is off. That battery is recharged from the generator when the engine is running. So any power taken from that battery, requires more power from the ICE to recharge the battery. Again, no free energy.
Air conditioning usually connects the AC compressor directly to the engine shaft (via belts). Again, when it is running that puts a drag on the engine's shaft, requiring more fuel to be burnt to keep the car going at the same speed. (The AC needs a lot of power, so this design avoids the inefficiencies of having the generator drive a big electric motor to drive the compressor. It also avoids the weight and space for a big electric motor).
icelandichorsey t1_j6db5h2 wrote
What else is powering them?
trootaste t1_j6dbqne wrote
Haha I realise it's a silly question, I was more asking how it powers them, not if it does or not. I know it's not plugged into mains
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