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Hydrogen gas fuelled cars are fairly efficient, petrol driven cars have been around for over a century and have basically peaked in their development.

There is only a finite amount of energy in fuel to be extracted to begin with. That places an upper limit on what your MPG can even be. So it can't simply go up forever without limit. And Whatever that limit is, there are diminishing returns meaning you get less and less an improvement over time.

Compared to what I was driving in the early 1970's theyare much more efficient.

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Well the truth is, they have. It’s not night and day, as there are engineering and cost concerns that come with chasing improvements, and there IS a limit to how much power you can get from an ICE, but they are improved. But most of the improvements so far are weighed down, literally. Newer cars ar heavier, with more power output, and more features, and that all brings efficiency back down. All manufacturers could have 50mpg cars out ther tommmorow, but that’s not what the market wants.

>why haven't gas powered vehicles gotten that much more fuel efficient??

Petrol engines have. e.g. The 1 litre, 3-cylinder Toyota engine has been available in various Toyota, Peugeot, Citroen, Daihatsu cars for 20 years or so and will easily return 60 mpg.

You just don't see such 'city cars' in the USA because no red-blooded meat-eating christian would buy such a silly little vehicle.

They are more efficient, you are just missing some variable. The 2003 Accord curb weight was 2989lbs while the 2023 is 3239lbs. The 2003 Accord horsepower was 160 while the 2023 Accord have an horsepower of 192.

So the 2023 20% more powerful, weight 8% more, but is 11% more fuel efficient than the 2003 Accord. So the 2023 engine is much more efficient than just 11% since it have more power and it need to power a bigger car. If the 2023 Accord would have the same weight and power as the 2003, the engine might be like 20-30% more efficient (I don't know the exact number just a guesstimate)

Internal Combustion Engine by their nature is pretty inefficient. You can explosion happen to push piston, so obviously a LOT of energy will be lost in heat. There is just no way to get around that. We are getting better, but the ICE is a very mature technology, improving the efficiency is harder and harder to do.

Are you using UK mpg or American mpg?

Because, of course, those are different.

Doesn't change the argument, but makes it less mind boggling.

Check the horsepower and weight. I suspect the new car is heavier and more powerful while getting better mpg. Consider what they could do if the really wanted higher mpg.

Because they’ve maintained the same mileage but vastly increased performance and probably vehicle weight. The engines have become more efficient but they’ve offset that by incorporating more performance, options, and safety features. Pretty sure they could build a tin can that would get a 100 mpg at this point.

Kind of like how a horse can only run so fast no matter what you feed it.

I haven't the faintest idea what a US or UK gallon is so I leave that conversion to you. I'm just using the manufacturer's quoted figures, via wikipedia.

I can tell you that I only fill up my Citroën C1 4-5 times a year.

Do you meaning hydrogen combustion or fuel cells? Those are completely different processes.

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Was trying to highlight the stupidity of using gas as an abbreviation for gasoline.

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.

There's a bit going on here.

Firstly, the US has a habit of buying big cars, and they've been getting bigger over time. If you add big, you add mass. If you add mass, you reduce fuel economy.

Second, regardless of the size of vehicles increasing, they've been getting heavier due to added structure for crash safety, additional safety systems, as well as added equipment in the vehicle.

Third, ignoring the way that fuel economy has been officially measured has changed over time (so you can't compare official figures separated by 20 years), traffic has increased which results in more stop / start traffic, which means worse fuel economy.

Edit:

I'll add a number 4:. Fuel costs by and large in the US over the last 20 years haven't been a major concern to consumers.

And 5: US federal policies haven't put major pressure on manufacturers to produce more fuel efficient vehicles until relatively recently. A lot of the rest of the world has spent the last 20 years pushing heavily towards reduced emissions, which has had a knock on effect of improved fuel economy.

Ok, it's commonly used in the US. Different countries use different words for different things.

Calling a liquid fuel gas is just silly.

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Hybrids are gas powered vehicles. They have electric motors powered by the engine that allow for better fuel efficiency and regenerative braking. My Prius gets 65 mpg on a good drive on the highway.

Edit: The same issue happens with the Prius though. The gas mileage isn't much better than the original. It's due to weight. The current Prius is over 300 pounds heavier.

>You just don't see such 'city cars' in the USA because no red-blooded meat-eating christian would buy such a silly little vehicle.

I'm taking a guess you're european and have no clue why cars are different in the US. We do have those cars, but commutes on average are at minimum twice as long as European counterparts. I don't think Europeans have ever actually looked at a map or globe critically when they say garbage like this. They don't understand how big the US actually is and how much distance MORE a US driver travels. this is why they buy the larger more comfortable models mostly, which has lend to an escalating war of leg room, comfort, etc.

Silly? Languages don't really have strict rules on naming things. Why use petrol for gasoline? There are a lot of petroleum products, but we only burn a couple specific formulations in cars.

It runs for longer, not faster

Whoosh!

This is why only dingdongs believe that the oil industry bought up special 100mpg carburators. There is only so much energy in a gallon of fuel and it's going to take x amount of energy to move a weight down the road.

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Headlights on all the time.

I understand your point that the name is not logical. I understand the states of matter. My point is that languages aren't always consistent. No one gets confused about the fact that gasoline is actually a liquid.

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The maximum efficiency of an ideal combustion engine (Carnot cycle) is only 50%. This is a theoretical limit, no real engine can actually reach this efficiency. The fact that we have engines in the 30% range is already pretty impressive.

Why aren't the improvements bigger? Well, because the closer you get to that limit the harder it is to get closer to it. In other words, it takes increasingly bigger technological and engineering advances to make increasingly smaller improvements to efficiency as you approach that limit.

Someone’s still salty about 1776 I see. /s

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Of course it does. That's what the alternator is for. That plus keeping the battery charged up.

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Yep. The engine powers the alternator which generates electricity needed for the rest of the car.

Fuel injection helped alotcwith that

There you go. First person to have the correct answer!

When the car is off the power comes from the battery. The batt gets charged by the alternator when the engine is running.

I’m the early 80s, Datsun hatchbacks were rated at 42mpg Highway. In the late 20’s you could achieve 25mpg in a Ford. Neither was very safe or luxurious though.
While I’m amazed by the low emissions of modern engines, we should have better mpg by now. Too many amenities, weight, etc on newer cars for my taste.

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.

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.

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?

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).

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.

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Why the heck is a Honda accord 1500kg, that's nuts.

What else is powering them?

FWIW the electric motor isn’t powered by the engine directly. That would be less efficient than the motor driving the wheels directly which is what they do.

It’s used for regenerative braking and then the battery power is used to run the motor.

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.

Because it's a full sized car now. The civic is larger than accords from a couple of generations ago

Safety. Airbags, crumple zones, ect.

and who wants to buy a tin can where there is no coffee/phone holder or help keep your butt warm, comfort adds weight

Much of the weight is driven by federally mandated safety standards

I think this guy answered his own question. Gas only vehicles can only be so efficient... Thus the hybrid.

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

Nothing like chemistry and physics to put a damper on a good conspiracy theory

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.

So, you've driven a Tata?

Nobody asked for more power though. Besides high schoolers, nobody is getting accords for power/speed . I want that more efficient engine in lighter weight body to maximize efficiency.

If it’s heavier, you need more power for the same performance.

I'm sorry you guys in North America don't have diesel options for most cars, not unusual to have a hatchback in Europe that can achieve 60+ mpg my 1.6l diesel 4x4 crv gets 55mpg. Not as many cool sounding v8s here tho 😄

As pointed out they are, but the market will not really pay for them.

The manufacturers make more profit on large higher performance vehicles, and have had to sell their smaller high efficient vehicles at a loss for years to meet their fleet efficiency standards (CAFE requirements). It does not cost 3x as much to make a $90k car as a $30k one.

So the typical efficient car buyer is not really interested in paying for efficiency, they are buying on price.

Dude specifically wrote "City cars" in his answer . . .

Safety requirements have risen. Cars are required to survive higher speed crashes with less injury to passengers which means more air bags and stronger construction. Then added tech plays a role, a rear camera by itself doesn't weigh a lot but add supporting bracketry, wire harnesses, and the computer power to render it and you get a few pounds multiply that over every new piece of tech and it adds up.

1. A lot of cars are just bigger than they were 15 years ago, comparing within the same segment of any type of vehicle.

2. Cars have way more airbags built in now compared to any time in the past

3. Most cars have way more electronics now, again compared to any time in the past. Cameras, blind spot sensors, tire pressure monitors, general “infotainment” systems

But there's a similar situation going on with hybrids. The 2023 Prius gets slightly better fuel economy as the 2003 Prius. It's gone from a 1.5L engine to a 2.0L engine over that time. The 2023 is 350lbs heavier, explaining a lot of the stagnation in fuel economy.

Yep... I just rode in a brand new civic and didn't realize it was a civic until I got out and saw the badge... Assumed it was an accord.

Also, there just isn't that much more you can do with an ICE engine - it's burning fuel to raise the temperature to generate overpressure which pushed pistons that turn "pedals", which then act through a complicated set of gears and linkages. Whatever you do, it's never going to be super efficient, most of the energy is lost to heating the coolant. And it's a technology that lots of people have already spent a lot of effort on optimizing, meaning most out the easy gains are long gone. Also, it needs to be fairly light and cheap to fit in a car, and work at a wide range of RPMs, torques, power levels, and it has to be reliable and not too complex.

So true! Also cars come with a lot more airbags, safety features and entertainment features than they did 20 years ago.

I‘m not sure I agree you on “nobody asked for more power”. A lot of people don’t want a sluggish car when they are trying to merge. People “ask” via their buying patterns. They’ll look to a V6 if the 4 banger is too puny. They‘ll look to a competitor.

Mercedes AMG reached 50% thermal efficiency with their Formula 1 engine about 5 years ago but your point about no “real” engine is still very valid. The F1 engine is using hybrid tech to reach that and is more expensive that many homes, let alone cars. They also are not using standard fuels or oils either. The engine reaches that thermal efficiency not while idling or going at low speeds, it does it at full throttle producing over 1000hp so, while fuel efficient in relation to other F1 engines, I wouldn’t be surprised if the semi truck used to transport the cars from track to track get better MPG.

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A lot of non performance low cc motorcycles get near that mpg. Like the Honda rebel 500 can get 65 I believe, the rebel 300 gets 75. The grom, monkey, and ct/trail can achieve 125mpg.

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are there also external combustion enignes?

I'd add that there's also limitations placed on absolute efficiency caused by other emissions restrictions; doi: 10.1109/TVT.2015.2405918

A long time ago, this is what ultimately killed gas turbine cars. They were pretty damn efficient for the time but the high combustion temperatures led to greater NOx emissions. The same issue is holding up the development of more efficient high compression ratio piston ICEs.

I got the v6 accord for power, speed, and reliability. Almost 300hp with a manual is a lot of fun for a daily commuter.

They actually are.

If you compare a car of today with a car from 20 years ago with the same power and weight the one from today will be a lot more efficient.

We don’t really notice much difference because cars today are much more powerful and faster than before.

However a Mercedes c class is faster today than Lamborghini from the 90’s, and also much more efficient.

1979 Honda Civic got 55mpg then.

The steam engine is an example.

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You don't want that lighter weight body, though, you just think you do. With the lighter weight body you lose a lot of safety features. You have fewer airbags, fewer crumple zones, fewer sensors giving you information about your car and road conditions. Modern vehicles sacrifice that slight bit of efficiency for a much, much safer driving experience.

1. By their nature, ICE engines are only about 20-30% efficient. Meaning 70% of the gasoline that is burnt by them is lost as heat. Formula 1 ICE engines are about 50% efficient, but these engines literally cost tens of millions of dollars and need a specialized team of engineers just to start the motor.

2. Cars have gotten heavier, the engines are producing more power, and despite this they still get better fuel economy than they used to. So they have gotten more efficient when you consider all the variables.

The overwhelming issue as to why we can’t have a 100 MPG 3500 pound car is simply that by design ICE engines aren’t that efficient and we’ve almost reached the practical limit of what we can do with them.

We’d have to switch to a different kind of engine/fuel like nuclear powered cars.

That's interesting, I'll have to read up on that. This limit is for purely thermal engines that run on a hot and cold heat transfer cycle. So I can imagine something hybrid would do better, but I'd be willing to bet that if we took a close enough look at that engine we'd find the thermal only part of the engine being under 50% efficient, and the rest was boosted by a different system.

1990 Toyota Tercel checks the boxes too. It felt like I was driving a go cart with windows. Had to kick off the AC to get to highway speed fast enough.

Some cars do gain a few MPG when you go for lower / base trims. I know the Kia Niro and Hyundai Ioniq (not Ioniq 5) do.

2/3 of the energy of an average ICE is lost as heat and noise. The main limiting factor is the size constraints of ICE don't allow it to use that heat the same way a power plant can, hence why round trip fuel /carbon efficiency of BEVs are so good even when the electricity comes from fossil fuels.

>nobody is getting accords for power/speed

True, but speed isn't the only reason to have more power. There is safety measure, but also luxuries. I like my divertissement screen, the GPS, the collision detection, the heating seat, etc. All of this mean more not only more weight to carry around, but also more electricity that come from the engine.

I also like to have a responsive car and a smooth acceleration, and for that you need more power. You don't really need to put the engine to the max to reach illegal speed on the road, but a more powerful engine change drastically how driving the car at low speed feel.

>I want that more efficient engine in lighter weight body to maximize efficiency

And there is other models that do just that. That said, those models are a lot less popular in North American compared to Europe so there isn't as much model available. Manufacturers sell what the market want.

Much of the increased fuel efficiency came from the addition of electronic modules to control nearly every system in the automobile… engine control, fuel delivery, transmission control, power steering control, etc, etc, etc. Each of these advancements have added a few percent to the overall efficiency.

For example, power steering used to be accomplished by a hydraulic power steering pump on the serpentine belt on the engine. When you were driving on the freeway at 75mph, you were barely turning the steering wheel. Most of the power to drive the pump was unused and wasted. Electronic Power Steering (EPS) instead senses the need and then controls motors as required, providing roughly 3% overall fuel savings.

This same approach has been applied to every system within vehicles. Rather than add weight, electronics increase the fuel efficiency while reducing weight. For example, the EPS modules and motors weigh less than the hydraulic power steering pump, hoses and hydraulics that used to be driven by the serpentine belt.

My first "new" car was an '86 Pontiac Acadian, 2 door. 1.6L inline 4 cyl with an automatic transmission that I quite literally drove like a go-kart. Would regularly take corners at speed by throwing the shift lever into "L", locking up the rear wheels, allowing me to drift into the turn, then back into "D" and nail the gas pedal to the floor.

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Only ever popped the bead on the rear tires twice. Fortunately, refilling them also reseated the bead.

Gas internal combustion engines are typically 18-23% efficient in terms of mechanical energy out vs chemical potential energy in. High performance and forced induction engines can to a little better than that but not by much. You lose a lot of energy through heat, sound, vibration amongst other things. Also emissions really damp efficiency but are obviously important. It would be cool to see a car manufacturer build the most efficient, light and not overpowered car possible to see just how much they could stretch the mileage.

No one, that’s why they’re engineered like I said now.

It's not really about the size of the country so much as how the infrastructure and cities are put together.

I haven't lived in a household that owned even a single car since the late 90s. We build our work and homes denser and closer together. So for a lot of things I can walk, and for everything else in and near the cities there's busses and trains everywhere.

Basically your culture choose to make you all dependent on commuting in cars. Mostly via the power of letting corporations decide for you.

It's just more profitable for them this way, you have to pay for the cars and the fuel and parking and the roads and the insurance and health care (because cars injure and kill soooo many people). And they profit from all of it. And they use that profit to fund politicians who promote and support it all.

Yep, absolutely. Air compressors for air suspension can take a fair amount of power, heated windscreens, the list goes on.

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.

>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.

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.

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.

The car has a battery that will run the accessories and be charged by the alternator when the engine is running.

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Hint: US cities are much much much more spread out and MUUUUCH larger than you think.

Hint . . . I live in Canada. I'm aware. Also aware that most trips in the US (~60%) are six miles or less. 17.5% in the 6-10 mile range. Another 8.5% fall into the 10-15 mile range.

5% are over 30 miles

5% are 20-30 miles

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So, what's your point?