Engine and A/C parasitic losses quantified

[Logic]

Originally Posted by Ecky

The 1.0L engine in the Insight weighs 58kg and has a brake specific fuel consumption of 215kg/kwh.

In the case of the Insight (a 26 year old car) the engine needed to primarily propel the car, most of the time. A smaller range extender might be used in modern vehicles that can primarily be driven on battery. It's certainly a question worth asking - do you put an engine in the car that's big enough, that the car can be propelled by it indefinitely, without running out of supplemental battery? Or do you pick some smaller size, such that the engine cannot keep up with the demands of cruise, but adds extra range? Do you build it to be highly efficient, or simply small and light?

The Insight's (26 year old) ICE is also 39% thermally efficient, compared with ~28% for the quoted engine. You get a roughly 24mpg or 10km/L improvement when cruising for an extra 50kg weigh penalty, with 26 year old tech.

According to your numbers 10kw is enough to do 100km/h on longer trips.
Not bad for a city car.
So not a too big or too small thing unless you want to cruise faster.


In a series hybrid city car with an engine almost always on policy:
Weight goes down by well over 50kg thx to:

• The smaller engine.
• The smaller, lighter, less costly main battery.
• A smaller, lighter(more aero) chassis thx to 1 and 2.

A 50+ kg lighter, a car around town is surprisingly more fuel efficient.

Now you're charging at traffic lights etc, but with an engine always at optimal load and rpm, rather than;
the second every now and then for 5 seconds in total, seen in std Urban Cycle tests.
At idle the engine is around 1% efficient IIRC, vs 30+% efficient, 100% of the time.

[Ecky]

Originally Posted by Logic

According to your numbers 10kw is enough to do 100km/h on longer trips.
Not bad for a city car.
So not a too big or too small thing unless you want to cruise faster.


In a series hybrid city car with an engine almost always on policy:
Weight goes down by well over 50kg thx to:

• The smaller engine.
• The smaller, lighter, less costly main battery.
• A smaller, lighter(more aero) chassis thx to 1 and 2.

A 50+ kg lighter, a car around town is surprisingly more fuel efficient.

Now you're charging at traffic lights etc, but with an engine always at optimal load and rpm, rather than;
the second every now and then for 5 seconds in total, seen in std Urban Cycle tests.
At idle the engine is around 1% efficient IIRC, vs 30+% efficient, 100% of the time.

You make a reasonable case, and I think it's worth consideration. I believe this is what BMW did with the i3, actually. It has a two cylinder 650cc range extender. Someone worked out the thermal efficiency to be around 28%. They're primarily driven as EVs, but can fall over to the range extender for longer trips. Due to the vehicle's larger profile, fuel economy is relatively lousy, even with the vehicle being made of carbon fiber and aluminum. Owners reported 34-36mpg on the extender.

On the latest Honda Jazz, Honda opted for a 1.5L with 41% thermal efficiency, or near 200g/wh. At highway speeds, the engine isn't at 100% duty cycle, so they might have downsized it slightly, but fuel economy would have suffered if a grade needed to be climbed. The Jazz has a rated fuel economy of 3.8L/100km (combined), or 62mpg US.

Both seem to be reasonable solutions, with different strengths and weaknesses.

[Logic]

Originally Posted by Ecky

You make a reasonable case, and I think it's worth consideration. I believe this is what BMW did with the i3, actually. It has a two cylinder 650cc range extender. Someone worked out the thermal efficiency to be around 28%. They're primarily driven as EVs, but can fall over to the range extender for longer trips. Due to the vehicle's larger profile, fuel economy is relatively lousy, even with the vehicle being made of carbon fiber and aluminum. Owners reported 34-36mpg on the extender.

On the latest Honda Jazz, Honda opted for a 1.5L with 41% thermal efficiency, or near 200g/wh. At highway speeds, the engine isn't at 100% duty cycle, so they might have downsized it slightly, but fuel economy would have suffered if a grade needed to be climbed. The Jazz has a rated fuel economy of 3.8L/100km (combined), or 62mpg US.

Both seem to be reasonable solutions, with different strengths and weaknesses.

NB that the BMW i3 REx's firmware can be modded to the Euro Spec, making the car much more usefull/capable!
The US version's firmware was downgraded to fit with some or other sucking fupid US regulation/s.
https://www.bmwblog.com/2021/02/02/c...ec-bmw-i3-rex/

AS for the Honda Jazz; one might disagree that : "economy would have suffered if a grade needed to be climbed".
Unless its one hell of a long climb, there's no reason the motor/s couldn't kick in a bit to keep the engine at optimum rpm and load.

IMHO
The oversize engines are there to keep idiots who do stupid things from moaning.
Stupid things like fully discharging the battery (bad for lifespan too) before switching on the engine.
The engine then has to be big enough to both; propel the car AND charge the battery.

eg:
Some Australian reviewer ran his camp site (TVs, fridges etc) off a BYD Shark's battery for a weekend, then hooked up his caravan and went haring up a long incline and complained that it could only do 100km/h.
Had he had a brain and set the vehicle to auto start and hold charge at say 70% over the weekend....

I think GPS/map/congestion connected firmware that asks where you're going before you leave (with work, home, etc presets) would cover the idiot majority.
But never underestimate the ingenious ways idiots will find to uck things fup!

[Ecky]

In the case of the Jazz, it would need a bigger battery, but you're right. It has enough battery to travel maybe 2-3km on battery alone, or provide 6-8 minutes of very mild assist, before needing to be replenished.

Honestly, the packaging in the Jazz is so good, I'd buy one in a heartbeat if Honda gave it a larger battery.

The i3's solution is really "good enough", even if I'd want for the extra 40% fuel economy on the handful of times per year I'd ever need it. A vast majority of my driving could be on the battery alone, making the fuel economy effectively irrelevant. What has stopped me from buying one are a) the BMW tax, and b) BMW reliability. BMW owners seem to find it normal to spend every year what I spend over the lifetime of a car in maintenance. The odd tires, for example, are really cool in what they achieve, but they don't last long and they're silly expensive.

[Phase]

15 mpg drop with ac? thats terrible! my hyunda io ioniq hybrid only has a 1mpg drop with the ac on, ive done plenty of steady state cruise tests on the interstate over the years testing this. my ac is connected to the lithium battery. when i turn the ac on in hotter weather, the front grill shutters open up to allow radiator cooling, so that 1 mpg drop could actually be from the aero drag caused by the front grill opening, and not even the ac itself running...

[Ecky]

Originally Posted by Phase

15 mpg drop with ac? thats terrible! my hyunda io ioniq hybrid only has a 1mpg drop with the ac on, ive done plenty of steady state cruise tests on the interstate over the years testing this. my ac is connected to the lithium battery. when i turn the ac on in hotter weather, the front grill shutters open up to allow radiator cooling, so that 1 mpg drop could actually be from the aero drag caused by the front grill opening, and not even the ac itself running...

Any chance you could throw a clamp meter onto one of the A/C compressor's phase wires? MPG is a fairly terrible metric, as the number grows as the relative amout of energy used gets smaller. It wouldn't surprise me if newer vehicles had more efficient compressors, but without knowing watts to watts, we're just guessing.

[Ecky]

Originally Posted by Phase

15 mpg drop with ac? thats terrible! my hyunda io ioniq hybrid only has a 1mpg drop with the ac on, ive done plenty of steady state cruise tests on the interstate over the years testing this. my ac is connected to the lithium battery. when i turn the ac on in hotter weather, the front grill shutters open up to allow radiator cooling, so that 1 mpg drop could actually be from the aero drag caused by the front grill opening, and not even the ac itself running...

Following my curiosity, I went searching, and apparently people have measured this already:

https://www.ioniqforum.com/threads/a...-tested.37144/

It also depends on the ambient temp, sun or overcast and what temp you have set.
I don't know if its the same compressor in the hybrid as in the ev(but I would assume so), but usually it draws 3-500W intermittently(to maintain set cabin till temp). I thought id seen it use up to 1200W but thats probably in the winter when its running the heat pump.

Setting temp to 15°c and fan speed to max it uses up to 600W when i tested ten minutes ago. That would be about 5% of the power required to drive the car at 90km/h.

So, you're right. Assume 2000rpm (90km/h ish cruise), the Insight's A/C draws 1900 watts mechanically on the engine. Ioniq owners have measured 3-500w intermittent, making their A/C ballpark 3x more efficient. Or at least, it draws 3x less power. We don't know the comparable cooling BTUs.

I wonder what makes modern compressors so much more efficient?