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

Looks like we have EPA rounding errors at play. The 2021 turbo gets 1 mpg less combined, but is rated the same in highway and city. While the 2020 turbo has the same combined and city, but 1 mpg lower highway than the NA 2.5L. Compare Side-by-Side



But the design requirements for the engine to an ICE car is different than for the hybrid. The new Santa Fe hybrids and PHEV will be using this 1.6 turbo.

You watched more of it than I. The Reuters article sited in the OP Roadshow link stated Nissan gets this engine to 46% in the lab, and they recover exhaust heat for something to get to an overall efficiency of 50%. For a consumer product, the efficiency peak may drop to give way for reliability, but it should still be over what engines can get now.

Part of the reason for the higher thermal efficiency is that this engine will run on a lean fuel mixture. Will it require additional emission controls over another gas engine? The original Insight was lean burning, and it had a NOx trap like some diesels.

 

The part about the gen1 and gen2 insights is close enough for me. although I think the ways it's been described by the car owners is that it has a "lean burn range" that the driver can engauge at varibale RPM's per load with throttle. My description may be a bit off, but I believe lean burn is most noticeable in manual trans gen1 and gen3 and I believe I noticed it my HCH2 a few times too. But only a few times. It's like a glide in neutral with minimal power from the IMA. at least that is what I remember. And it's really not an important thing as there is not much talk about lean burn even by older enthusiasts any more, that I'm aware.
Thanks for mentioning it

 

Relax my friends as a lab engine is not an assembly line part. It is common to find some MBA manager willing to screw the future for his personal gain.

Bob Wilson

 

One f1 innovation is a jet ignition, which can use a lean burn in the combustion chamber to be more efficient. I think this is what Nissan is probably doing in the lab.
MAHLE Powertrain | MAHLE Jet Ignition

Mercedes uses this and the e-turbo for exhaust heat recovery in its 50% efficient f1 engine. Garrett is going to start selling the e-turbo. Now the reason I predict Nissan needs SCR after treatment is that to get it street legal at 50% efficiency, is that mercedes to comply with emissions requirements dropped efficiency to 43%. Still I'm sure in an easier application nissan can get it between these numbers and not need the after treatment.

 

Bingo!

Unrounded numbers from EPA's detailed datafile:

2021 Turbo : City 26.7781; Highway 36.6747; Combined 30.4792.
2021 regular: City 26.8552; Highway 36.8145; Combined 30.5776.

Highway numbers differ by 0.14 mpg, City and Combined differ by less than 0.1 mpg, but a single of those pairs straddles the rounding boundary.

Beware that there are a couple more versions in the mix with larger differences.

Larger offsetting differences are seen here:
2020 Turbo : City 27.4682; Highway 35.5127; Combined 30.586.
2020 regular: City 26.8552; Highway 36.8145; Combined 30.5776 (same as 2021).

 

Honda was doing lean burn long before hybrids, and I believe they've had consumer engines running with the leanest fuel mixtures. The challenge of getting lean burn is in getting the fuel mixture to ignite. In a typical engine, have too little fuel in the cylinder, it can dilute out to the point that the spark won't ignite it. In the VTEC-E engines, Honda directed the incoming air to the cylinder to keep the fuel concentrated near the spark plug during lean burn. I don't think it was possible to run lean for the entire span of engine speeds, plus running lean meant reduced power. So the lean burn only occurred while maintaining a speed.

The reason we don't see lean burning engines any more is because of emissions. Out of the engine, lean burn actually produces less NOx and hydrocarbons as they are mostly completely burned. The problem is that the 3-way catalytic converter needs the NOx, CO, and HC pollutants with in a certain ratio in order to treat them all. This happens when the fuel mix is around stoichiometric. While the lean mix has less NOx in it to start, the cat is unable to neutralize it, and overall NOx emissions climb. With a NOx trap, the Insight would catch the NOx burning lean burn, and them release it while the engine was running with rich conditions.

Catalytic converter - Wikipedia

Sounds like Nissan's STARC is different, but then the descriptions out now are short on the details. It does seem lean burn is an important part of the increased thermal efficiency, and getting those conditions in the engine are only in a narrow operating range, thus why it will be used with e-Power.

"To achieve 50% thermal efficiency, Nissan developed a concept called “STARC”—named after the key words strong, tumble and appropriately stretched robust ignition channel. The concept enables improvement of thermal efficiency by strengthening in-cylinder gas flow (the flow of the air-fuel mixture that is pulled into the cylinder) and ignition, reliably burning a more diluted air-fuel mixture at a high compression ratio.
...
In internal testing, Nissan achieved a thermal efficiency of 43% when using the EGR dilution method and of 46% when using lean combustion (excess air ratio of λ = 2) with a multi-cylinder engine. A level of 50% was achieved by operating the engine at a fixed RPM and load combined with waste heat recovery technologies."
Nissan reaches 50% thermal efficiency with next-generation e-POWER system; STARC - Green Car Congress

A NOx trap alone isn't going to work if it's lean burn all the time. Guess it comes down to costs as to whether a US version will be detuned for no lean burn, or using SCR. I think the markets that will get e-Power are also less strict than the US in regards to NOx. An e-turbo would seem to be a no brainer for a series hybrid.

The 1.6T does produce 14 more ft-pounds of torque down at 1500rpm vs the 2.5L's peak at 4000rpm, so it will feel 'faster' to many drivers despite a 9hp lower rating.

 

read the article. it seems very promising. though to me when they explained a bit about the STARC and said it was unclear what exactly the new waste heat technolgies were, i feel its just mumbo jumbo word tech that just means "we got last years data and are able eto adjust variables with current tech". didnt feel that spectacular. but whatever works for stock prices though? i just hope this tech will come to the US soon (it says it has not?), i am very interested on its impact.

 

e-Power hybrids have only left Japan recently. You can get a Kicks in Thailand with it. As a series hybrid, the system likely won't do to well on the higher speed EPA tests. Then we have cheap gas, which makes hybrid cars a tough sell. Going the power hybrid route here might be more successful.

 

@Trollbait After posting above, I thought my description of lean burn in gen1 and gen2 insight with the 3 cylinder 1 liter ice, sounded to me to be very similar to how pulse and glide works from the controls in the cockpit.

Than reading your post just above, (second up now) before I'd gotten to your mention of V-Tec that is what I thought of, after reading the first line.

Than reading the second line I thought of the HCH2 4 cylinder 1.3 liter with eV-tec and 8 spark plugs.

My 02 civic ex 1.7 liter has v-tec also, and I've done a bit of research on some of the more recent iterations of variable value timing implementations by other manufacturers, but I'm not up to speed on the history.

In your second sentence - if I may "The challenge of getting lean burn is in getting the fuel mixture to ignite. In a typical engine, have too little fuel in the cylinder, it can dilute out to the point that the spark won't ignite it."
from a non engineering point of view, that one sentence sounds like the basis for better thermal efficiency of an ICE. Not to mention all the other subsystems to maintain the critical operating temp internally through a fairly dynamic ambient temp range.

 

gen1 and gen2 insight 1 liter 3 cylinder also have oem numbered stark plugs specific to each of the 3 cylinders. Which I initially thought was a strange and my 1.3 liter 4 cylinder with 8 spark plugs.

 

VTEC is Honda's brand for variable valve timing.There are several variants. The -E seems to be the only one with a lean burn mode. It was available on the gen5 Civic(VX trim), gen6 Civic(HX), and gen1 Insight. As I mentioned, the Insight needed a NOx trap like a diesel to pass inspections, and because of that, I think Honda stopped using it, at least in the US. I think the CR-X HF had a lean burn mode, but can't say if it had VTEC.

Double spark plugs isn't uncommon on 4 cylinder engines; I know that was the case with original Ranger ones, and a quick search shows Dodge Hemis also have two per cylinder. The reason for it on cars is that it ensures a complete burn of the fuel charge and helps with emissions. They may not fire off at the same time.

I find Wikipedia is a good place to start.

The Hyundai engine brought here keeps the engine block and head at different temperatures through different coolant loops as part of its suite of efficiency methods. Not a new idea, but I think the first time in a mainline brand.

Interesting, the gen1 Insight had spark plugs indexed at the factory. Some modders, for power or efficiency, will do this to their engines. It means having the open gap of the plug facing the intake valve. Not having the spark blocked by the post means most of its energy goes to igniting the fuel.

Modders use washers to get that gap facing the right way when the plug is installed. Honda stamped each cylinder with a letter, and using the plug with that letter meant it had the right facing when installed. The plugs are the same, just where the incline of the screw starts in relation to the gap is different.

 

I was a bit interested in the NOx trap thing and at the bottom of the wikipedia search page using "nox traps" was this page on combustion Combustion - Wikipedia which I thought I should read as a refresher this morning. Since I thought when reading in the post above about NOx trap that it would be part of one or both of the cat1 and cat2. Not all that interesting in and of itself, for me anyways. At least if not also interested, as I was, in the Miller cycle as mentioned by @austingreen above and the differences of Miller, Atkinson and Otto cycles, which I also wiki searched out a few days ago when I read that post. (patent dates, diagrams, versions or Atkinson, their popularity over the last century as they also relate to emissions issue we all struggle to understand presently in this new age of quantum mechanics and advanced thermodynamics, etc that some of the best minds alive are working to understand more thoroughly. I wish I was one of them, sadly and a bit frustrating at times, that ship sailed a lloonngg time ago,

 

Actually that sounds the same to me as turbulent jet ignition (TJI). The combusting rich fuel air mixture from the pre combustion chamber enterers the cylinder from small holes (4 or 8 usually) that tumble the incoming flame/gases through the cylinder causing a turbulent flame front. A check this morning had Nissan (GTR), Toyota (Supra), and Honda (NSX) using this type of tech in their Super GT 500 race cars. This Japanese racing series uses turbocharged 2L I4. Mahle parts supplier to Mercedes and Ferrari specifies their tji system can work with lean ratios with a lambda greater than 2 just as in the Nissan blurb. TJI definitely gives you a stretched robust ignition channel as the jets stretch from the pre-chamber through multiple holes in the cyclinder to provide a large volume for ignition.


Of course Nissan could have found a different way to do this in cylinder and Nissan in their car says they are using a regular spark plug in the preignition chamber so they are likely doing something slightly different than the mahle's f1 implentation. The article was from 2018 so they probably had race cars with the engines in 2018 or 2019 and a great platform to experiment with valves, native compression, percent lean, and optimal turbocharger for an efficient 2L engine.

The higher the effective compression the more efficient an engine will be and the more NOx for any given design. Nissan may have solved the problem but my guess is NOx will be high in any 50% efficient miller cycle engine.

 

Is this a Miller cycle? The term forced had me thinking there was a charger, but I didn't find evidence with the skim of the video.

 

Where I sit in Virginia the government speaks with forked tongue. They apply a surcharge on vehicles getting more than 23 mpg while mandating a deadline for moving to all EV.

 

I don't find that inconsistent. They want the money to maintain the roads (and people downstate have always done well when the funds are allocated). Those roads are still going to be needed when all those heavy battery laden vehicles use them. They are struggling in NOVA with emissions levels. Then there is that whole climate change thing. So pay me now and change later. At least they aren't singling out hybrids and EVs for special treatment if they say all vehicles over 23 MPG

 

So charge that at the city/county vehicle tax level. We do not have as big an issue in rural central Virginia.

 

The extra weight of the batteries isn't going to cause more damage to a road designed for commercial trucks.

 

Do you have a source for that? We are talking half a ton of batteries or more in some of these cars. The street I live on was not designed for commercial trucks. There is a sign at the entrance to the neighborhood prohibiting them. The only big trucks traversing the street are garbage trucks, utility trucks, etc.

 

Even those garbage and utility trucks are far heavier than residential BEVs.

Numerous prior threads here have pointed to or discussed transportation industry findings that weight-induced roadbed damage is a fourth-power function of axle load. With that 4th power in the equation, a ton added to a common passenger car, or replacing a medium car with a full size SUV, is still negligible compared to running a 10 ton to 40 ton truck.