Featured Smaller engines at risk due to real world test results?

I would assume the Price family safe from this debacle?

Posted via the PriusChat mobile app.

 

Thousands of times more emissions per gallon are made getting petroleum out of the ground and to your door, plain stupidity to worry about making more clean exhaust over using less fuel

 

It was expected, if someone spend some time over Spritmonitor values...because NEDC was a theoretical result and focused on lower power outputs.
WLTP soon to be adopted, will show the efficiency flaws of the small engines regarding highway road power bands.
Just recently I crossed Ford Fiesta 1.0 ecoboost 100cv against Toyota Yaris 1.3 99cv, and guess what...the little 3-in-line turbo loses to the 4-in-line-NA. Can't wait for the WLTP to give justice and honesty to the european auto market.

 

The Prius family is very, very safe from this.

So, essentially, the current European testing regime is very, very gentle on the cars... but it kinda has to be. See, it needs to be gentle enough that the slowest cars when it was developed could pass the test, but in 1990 (when the extra-urban portion of the driving cycle was added), you could get some horrifically slow cars in Europe. Like, we're talking about 0-60 MPH in 30 seconds levels of slow.

This means that a very small engine is all you need to complete the test, and we all know that very small engines can be incredibly efficient - they have less frictional losses than larger engines, and they have less pumping losses at partial load than larger engines, all else being equal. So, if you can get consumers to buy a smaller engine, you can complete the test with those benefits. (Pumping losses are largely a side effect, by the way, of having to restrict the amount of air going into the engine, as you don't want excess oxygen - too much oxygen means that heat inside the engine will cause the nitrogen and oxygen in the air to react, and form nitrogen oxides, which are involved in smog formation. Diesel engines for various reasons can't practically do this, which is why nitrogen oxide emissions are such a problem for them.)

However, consumers in 2016 don't want to buy a horrifically slow car that will get beaten off the line by a bicycle. And, those small engines make less power, of course - an engine's power is determined, essentially, by how much fuel it can effectively burn in a given amount of time, and that's fundamentally determined by how much air the engine has available to burn that fuel. Smaller engine, less air to burn, not able to burn as much fuel.

The solution is forced induction, in the form of turbocharging typically. So, a turbocharger is a device that has a turbine wheel that is spun by excess exhaust energy. That wheel then spins a compressor wheel, which compresses air, pushing extra air into the engine. More air in the engine means you can burn more fuel. More fuel means more power. On paper, what this means is, when you're driving gently, you have the efficiency of a very small engine, but when you need to accelerate, you have the power of a large engine.

There's a problem with that, though. See, gasoline is a very volatile fuel, that likes to explode, especially if it gets too hot. Exploding at the wrong time can cause lots of damage... and making more power in a small engine produces more heat, and compressing the air heats it up, too. You can use an intercooler (effectively another radiator) to cool that compressed air back down before it goes into the engine, but you're still making more power in less space, and have heat to worry about.

The first solution is... if you spray more fuel than you need, when the engine's at its hottest, the fuel droplets will actually help cool the engine down from the inside. However, this means that you have more fuel than you need in the combustion chamber, increasing emissions and fuel consumption, so you don't do this all the time, only when the driver's requesting a lot of power... or, in Europe, where the engines are made as small as humanly possible, you actually do do this almost all the time, except when the driver's barely requesting any power at all - because the test can be done with barely any power at all, this means you can get incredible efficiency on the test... but it goes to crap as soon as a normal driver actually drives it in the real world.

The second solution is to use direct fuel injection. So, in most gasoline engines today, a system called port injection is used - fuel is injected in the intake port of the engine, mixing with the air as it enters the engine. This provides very good mixture, but it means that as the piston compresses the air, it's also compressing and heating the fuel, which makes detonation more likely. This limits how much compression the engine can do, and in turn, that limits how much expansion the burning fuel/air mixture is allowed to do before the piston reaches the bottom, affecting efficiency negatively. Direct injection, however, compresses the air, and then injects most of the fuel right when it's needed, right in the cylinder - the fuel can be cooler this way, and as it's injected when it's needed, detonation is far less likely. (Some systems inject part of the fuel before it's needed, for better mixture, and then the bulk of it right when it's needed.) The problem with that is, direct injection doesn't give time for the fuel and air to mix that well, increasing emissions - there'll be some hot spots on the edge of a droplet where there's not enough fuel, increasing nitrogen oxide emissions, and some cold spots in the middle of a droplet where there's too much fuel, increasing soot emissions. Combine that with excessive fuel being injected to help cool things down, and you get a lot of soot emissions.

The Prius engines are trying to solve some of the same problems, but use a very different approach. Instead of making a smaller engine, they use what's commonly called the Atkinson cycle, but what it really is, is it pushes some excess air/fuel mixture out of the intake valve - this has much less pumping losses than just closing a throttle plate. Because air/fuel mixture is being pushed out of the engine for some of the compression stroke, you've effectively shortened that stroke (even if you haven't done so in reality), and can increase the expansion ratio (which helps efficiency, by getting more work out of the same fuel) without having to worry about detonation, making the Prius engine more efficient than a normal, smaller engine of the same power, despite the higher frictional losses of a larger engine. This means that the Prius can use a port fuel injection system, no direct injection needed. Also, the hybrid system on the Prius helps compensate for the permanent Atkinson cycle operation, allowing a less powerful engine to be used but still have acceptable performance. (It's also worth noting that these comments apply to most Toyota hybrids, not just the Prius, with the exception that some of the premium hybrids (some Japanese-market RWD Toyota hybrids, the current Highlander, and most current Lexuses with the exception of the CT, ES, and NX) have direct injection.)

It's also worth noting that Toyota's approach in general has been fairly conservative on this front - they've adopted direct injection on some engines, but usually (with two exceptions that I'm aware of, a 1.2 liter turbo 4-cylinder for Europe, being used where a 1.6 or 1.8 liter naturally aspirated 4-cylinder would normally be found, and a 2.0 liter turbo 4-cylinder used in Lexus models everywhere, replacing 2.5 liter V6s and 2.7 liter 4-cylinders) without turbocharging. Their direct injection system also includes a secondary port injection system, which helps some with the emissions impact. They have adopted wide-range variable valve timing systems that allow them to switch an engine between normal operation and Atkinson cycle depending on what's going on, in that aforementioned 2.0T motor, and a 3.5 V6 motor used in the Tacoma and Highlander/Lexus RX 350 (I believe that's technology licensed from Mazda). Many of their models are still old-school port-injected motors with nothing fancy at all going on, and they still sell at least in less fuel-pricing-sensitive markets. Many of Toyota's most efficient engines are port-injected, too, both ones specified for hybrid applications (like the ESTEC version of the 2ZR-FXE used in the Gen 4 Prius, one of the most efficient gasoline engines of all time) and not (like the 1NR-FKE used in many European Yarises).

Funnily enough, because Toyota's lagged behind the industry so badly in the whole "downsize and turbocharge" trend, it means that they're one of the automakers that's the best positioned to capitalize on the trend backfiring - they've still got plenty of large displacement engines, and their platforms are still designed to fit large displacement engines.

 

Thank you for that excellent explanation!

Posted via the PriusChat mobile app.

 

i'm just glad we're getting some real world testing. i'm more concerned about air quality than engine size. they'll figure it out eventually, hopefully, without cheating.
oh wait! i have a solution: bev.

 

Actually your Gen 1, PiP is (was) a good start at the time and the future Prius Prime even better.

I live in a fly-over state, Alabama, and completed a 463 mile trip Charlotte NC to Huntsville and round trip, 700 mile each way, Huntsville AL to Stillwater OK over the Labor Day weekend. It would have been impossible in any BEV in less than a week. The fast-charging infrastructure in rural USA does not exist and there is little evidence it is being built anytime soon.

Bob Wilson

 

aye, there's the rub for conventional carmakers. let the whining begin!

 

I am amused by the title of this thread when my daily driver has a non-turbo, 647 cc engine. ROTFLMAO.

Bob Wilson

 

To be fair, that's not what's meant by "smaller engines" - a 647 cc non-turbo engine is actually what's in the spirit of NEDC, very slow cars.

 

I have 168 hp, rear wheel drive that might take exception.

Bob Wilson

 

Right, but once your battery's at minimum SoC, then the behavior is much closer to the weak city cars and city vans that the NEDC was designed for (until the vehicle is driven slowly to recover).

 

Which is why coding to allow SoC maintenance early is so important. It makes it work.

Bob Wilson

 

I am confused if the article is mostly talking about Europe/diesels.
Are we saying FORD/Hyundai hybrids are not working re: real world emissions?

 

It's mostly talking about Europe, yes, but both gasoline and diesel engines.

 

The only difference is my model says that with a sufficiently strong EV train the actual loss is aerodynamic and rolling drag and that can be made smaller than all but BMW and Toyota have figured out.

Bob Wilson

 

A very interesting graph showing this outrageous trend of real cheating FE:



source: http://www.theicct.org/blogs/staff/tren ... ssions-gap

 

you get a major spanking here in SoCal for that stunt (not that I'd ever suggest folks un-code just prior to smog inspection ... maybe VW could loan their software to auto deactivate when the i3 is on the dyno .... )