Featured Nissan claims it's made a more thermally efficient gas engine, but there's a catch

The Nisan idea is to run at a set speed for which it has been optimized. But reading further, they run in a range from 2000 RPM to above 3500 RPM. That implies that they are making some concessions to get enough power when needed without increasing the engine size.

 

In theory, a series hybrid with battery could have the engine run at peak efficiency all the time. Any excess energy made goes into the battery, and when the pack is fully charged, the engine shuts off. Designing for a series hybrid also lets you optimize the engine's operation of a narrow range of engine speeds.

There was an early Audi e-tron concept being developed pre-Recession; it was an A1 PHEV series hybrid. They might have had a dozen test cars running before shelving it. The engine was a rotary that ran at one speed. At least initially, that was the design. With testing, they found some people didn't like the a single speed engine hum that was completely divorced from the car's speed. Before the project was cancelled, they had the generator run at three set speeds to better match the car's speed.

That could be what Nissan has done here. Then the battery is smaller than the one in a BEV. There could operation times when the battery is full, and system wants to use the engine(example: battery too hot) One of the slides in the video shows the engine has a wide efficiency 'sweet spot' that engine range is withing. So it may not be much compromise to having a wider operating speed range, whatever the reason for it.

 

I'm not a chemist nor a mechanical engineer, but isn't it generally true that there is one and only one spot where an engine is most efficient? Basically the point where you get the most possible power for the fuel that is consumed? Unfortunately that point is often not the place where the emissions are lowest. That was a problem with the early Wankel engines. They had lots of power at high RPMs but also had high NOX output.

I suspect (based only on the way that it fits the scenario) that the system is designed to feed the electricity directly from the generator to the electric motors where possible in order to avoid losses from charging and discharging the battery. If the battery is undersized, you end up with cases like accelerating onto the freeway or uphill where neither the engine (at low RPM) nor battery has enough energy for the job. If the torque is reasonably constant you can up the RPMs by 50% and get 66% more power. That's assuming the generator is not already maxed out when the engine is running at 2000 RPM.

Dan

 

In the Prius engines, particularly Gen3+, that one-best-spot is surrounded by a fairly broad plateau of near-peak efficiency. It is high- and flat-enough that it often makes more efficiency sense to adjust the engine power around that plateau to fit the current direct power need, than to run at only the very-slightly-highest point and then pass any excess through multiple energy conversions (generators, motors, inverters, battery charging, and battery discharging). Each of those conversions adds a bit of loss, and collectively they will often exceed the loss of running the engine a bit off-peak.

 

There is a peak point of maximum efficiency, but engines have 'islands' of high efficiency. The size of these vary with engine type and design. I skimmed the video in the original link, and there was a consumption map for the new engine; the 2000 to 3500 rpm range was in the island.

 

This is great! I need to watch the whole YouTube video when I get a chance. I love the way the Japanese nod when they are introduced. It's funny though they are dubbed with female voiceovers. 50% thermal efficiency is great, and they have certainly put a lot of effort into this, and it is exciting. The current Prius engine is at 41%, and I think the Camry Hybrid engine is at 42% thermal efficiency. Hyundai's TGDI hybrid engine is also about the same. The next-generation Prius engine could see 45%.

 

I've searched and couldn't find any source for this.
Can you share?

 

Yes. The downside, however, is that, every time you convert energy from one form to another, you also lose energy.

Series hybrids convert energy many times:
— Chemical to thermal and thermal to mechanical in the ICE,
— mechanical to electrical in the generator,
— electrical to chemical charging the battery,
— chemical back to electrical discharging the battery,
— electrical to mechanical in the motor.

Yes, the conversion efficiency in all components above involving electricity are comparatively high, but they’re not 100% by any means. Will the extra ICE efficiency compensate enough for that? Possibly...

 

In my 2014 BMW i3-REx, the range extender sustains, does not charge the battery:

• Chemical to thermal
• Thermal to mechanical
• Mechanical to generator
• Generator to motor mechanical

The battery performs as a buffer for local high and low demands like climbing a hill and regeneration on the subsequent descent. The engine throttles to as needed to keep the battery SOC constant. Not perfect, the engine could be more efficient and waste heat captured for cabin and battery purposes.

Bob Wilson

 

Diesel (Wankel) is problematic for emissions because it is harder to clean up. .
For gasoline cars the emissions can pretty much be almost totally fixed with the 3-way cat converter.
3-way catalyst destroys most CO, NOx, HC hydrocarbons.

So the problem I see is USA: we want to say our policy is No ICE+ no PHEV's + no HEV hybrids, all 100% BEV. Part of the reason for that policy is probably GM/Ford do not want to compete with Japan autos in that hybrid space.

 

The Ioniq(and Niro) engine is 40% efficient, like the gen4 Prius.
Hyundai Ioniq - Wikipedia

Which is why a straight series hybrid's fuel economy doesn't do as well at higher speeds. Honda's two motor system, and the one in the Volt, favored EV use, but both still had a mechanical connection between the engine and wheels for higher speeds. The main reason we likely haven't seen e-Power outside of Japan is because of the more challenging tests in other markets.

Series hybrids offer other advantages. For Nissan, it is lower costs through reduction of parts. Instead of continuing the production of a traditional transmission for a parallel hybrid, or making an entirely different one for a power-split system, they just take the drive train they developed for BEVs with a smaller battery, and add a generator. They have the same approach to FCEVs.

For PHEVs, a series hybrid is easier and cheaper to add as a range extender. Right now, we are seeing power-split and parallel hybrids being made into PHEVs, because the company had a hybrid system for a non-plug-in. It works, and has its own advantages, but consumers will start asking for more EV range after having 25 to 40 miles.

That requires a bigger battery, but it is inefficient to put one into a traditional car platform because of the compromises needed. The best place for a large battery is under the cabin floor. There it takes away the least amount of usable space, and the weight is added to where it could actually help the car's handling. The majority of car platforms have a front mounted engine though. That means an under cabin battery needs to conform around a hot exhaust system. So the battery becomes smaller, or takes up space elsewhere. A rear mounted engine means its supporting systems can be packaged away from the battery.

Now, FWD with rear mounted engine isn't practical design wise; you lose the efficiency advantage of FWD. With RWD, the engine can be tied to the wheels. It would mean better efficiency at higher speeds, but this car is going to have an EV range around that of the short side for BEVs. The range extender may only be used on long trips. Having the engine connected to the wheels could mean an efficiency penalty for the EV side. It will mean a cost penalty for the transmission. A series hybrid system is just easy, thus cheaper, to add to a car platform designed for majority EV use. Yes, it will have a lower highway efficiency than another hybrid type, but the greater amount of EV miles means a large reduction in gas use anyway.

 

This is by no means apples to apples but we have
Compare Side-by-Side


2019 Honda Accord Hybrid vs. 2019 Toyota Camry Hybrid

The clarity phev and accord hybrid act as series hybrids in the city test. The accord and Camry get similar mileage in the city with the accord coming in between the Camry le hybrid and the other Camry hybrids. The accord though accelerates better at low speeds despite having a less powerful engine.

On the highway we can see the problem with series hybrids. The clarity phev does much better than the i3 rex. At speeds 45 mph and above (or something like that) the clarity phev and accord hybrid lock into a direct gear, while the i3 is still in series mode. If we scale the electrical efficiency of both the i3 and clarity then the i3 on gasoline is 81% efficient. engine efficiency could be part of that, the honda's engines have a peak efficiency at 40%, the Camry's at 41%. At higher speeds that 0.6 L engine must be eating into less efficient zones compared to the 1.5L in the clarity.

According to car and driver's test, on the highway @75mph the toyota's psd and larger engine get 2 mpg more than the accord hybrid with its single speed transmission that is likely set for a lower speed. The camry hybrid with its hsd transmission also accelerates better at speeds above 30 mph.

If we get to the efficiencies of tesla's switched reluctance motors then the genset and drive motor will both be about 95% efficient or 90% round trip. This in city driving may be more efficient than even a hsd type transmission. The hsd will run this way at low speeds though. Nissan though wants to run at constant power, or maybe two powers. Then we have to consider the round trip into the battery then back out and through the inverter. The more power that is buffered the bigger the losses. Still its manageable, but at higher speeds a lock up automatic transmission or hsd is going to use less power.

 

Plus wind resistance, of course...

 

Ioniq Engine | Hyundai Introduces New Engine in Dedicated Hybrids | WardsAuto

Hyundai Aims For 50 Percent Thermal Efficiency For Future Engines

 

I'm sorry, no mention about the TGDI. Those links are for the Atkinsons 1.6 GDI we already know.

 

Missed the part about it being a turbo. Seems the only hybrid with it is the upcoming Sante Fe.

I would be surprised if the thermal efficiency drops with the addition of the turbo. This engine is using all the techniques that got the Ioniq's engine that efficient, plus new ones Hyundai developed since then. A turbo might even improve this further.

People can end up with a fuel economy penalty with a turbo, but that has more to do with self control of the accelerator pedal than the engine design.

 

They could have just said "...but you'll be seen driving a Nissan" and saved us a lot of time.

 

Here is the first of the new Smartstream engines.
Hyundai’s 1.6L Turbo-4 Sophisticated, Remarkably Efficient | WardsAuto

On the sonata the turbo gets 1 mpg less than the normally aspirated version so I assume its less than 40%. They say in the lab they can get it to 50%. My guess given their research is that is in a diesel version that would be 50%, and would require SCR to make the engine compatible with US regulations.

Still they should be able to get more than the 40%, but that would likely require a different intercooler and turbo and of course make it a hybrid or phev to keep it in that efficiency sweet spot. Toyota said they had 45% turbo gasoline engines working in the lab.

Mercedes in project one which hopefully will ship this year has a 43% efficient version of their 1.6L turbocharged F1 engine that was 50% efficient. The reason it dropped so much as they wanted to keep it as close to the F1 engine as possible but needed to meet emissions control and drop the idle from 5000 rpm to something more reasonable. At 748 hp its a very expensive design. It should be fairly easy looking at that to design a 200 hp or 300 hp 4 cylinder engine that is around 45% but it will be expensive. After that those gains in efficiency are tough if emissions need to meet or beat todays targets.

 

I only could handle about half of the vid, and also read both the Tesla and Huawai articles underneath the vid since the beginning of the vid was so boring.
The Title might be a bit misleading, as the only part I heard in the vid that was about thermal efficiency was between minute 16 to 18.
At timestamp 17:28 give or take - The Catch - IMO was the translation that Nisson is working towards 50% efficiency in the future as an ultimate goal.
Did anyone else get that from the vid?

 

When I was in the R&D arm of the marketing arm of the local phone company, we learned to embrace certain terms. "Working in the lab" was a great one, since we could use $100,000 worth of equipment to provide a service for 100 customers that would only sell at the price point of 7.95 a month. It looked good in the quarterly reports.

We could do anything, and follow it up with "we expect to reach 75% in the coming year". There was no requirement to advertise that 75% was common for products already commercially available.

In short; marketing was evil and lied like a lazy dog in the summer heat.

Dan