Small engines vs. big engines?

[Topher925]

The reason that is becuase American car manufacturers have been horribly backwards with engine design. American manufacturers like cheap, with no regard to environmental cost.

One of the links you posted said its only the European manufacturers that use the turbo strategy. Every American AND Asian manufacturer currently are taking the NA route in general. And I wouldn't say American manufacturers are backward at all. The Ford EcoBoost is a fantastic engine that uses state of the art technology including a turbo. Its just very expensive and the NOx emissions can be high.

Turbocharged cars are complex and therefore are disregarded. They are stuck in a rut, American consumers hove your attitude to turbo motors, so manufacturer will make them for fear of not selling. The consumer can't buy them if no one sells a good turbo motor.

Engines in general are complex, with or without turbos. And I don't think most consumers are afraid of turbos. I always thought that was a big selling point for Saab's was that most of their models could come with a turbo.

This however is changing. Get with the times. Engine downsizing is the trend within the industry to provide the power and meet emissions standard , you will find it in the vast majority of cars world wide. If not this generation, then the next generation of cars.

I'm hoping the next generation of cars won't have turbo's because they won't have ICEs.

Ford is putting a 2.0L Turbo over it's V6 in the new Explorer. Similar power output with a boost in economy of aprox. 30%...

Yes, all very good examples, especially the Ford Ecoboost engine. However, you're not comparing apples to apples. All the engines in the links you posted include a lot more than turbo's to aid in fuel efficiency. I believe just about all "downsized" engines that use turbos also use direct injection or DISI which in itself accounts for huge efficiency improvements, I would argue much more than a turbo.

I think engine downsizing is going to occur which will include the introduction of turbos and direct inject into cars. Both technologies compliment each other extremely well. But I didn't think that's what we are talking about? I thought this thread was about more classical engine tech that used port injection like your average car. If this isn't the case, then you should also be comparing NA engines that use the Atkins cycle, variable valve technology, and direct inject.

The advantage comes from the fact that you are running the turbo (ie compressing the air) with something you would otherwise just throw straight out the exhaust and not something you want to use. It's like adding an LP turbine to a power plant to take advantage of the energy still left.

No it isn't. A turbo doesn't use any wasted power with the exception of power that is extracted from exhaust gas expansion. When you add a turbo to an engine, the pistons have a greater exhaust gas pressure due to the obstruction that the turbo creates. In other words, the engine has to work harder to push out the combustion products on the exhaust stroke. This is by no means "free" power which a lot of people like to believe.

The power extracted from the thermal expansion of exhaust gases can be determined by measuring the temperature difference before and after the turbo. However, heat transfer needs to be taken into account as well. That impeller spinning at over 100K rpm has a very very good convective heat transfer coefficient.

Not only that, turbo cars a far easier to drive. As they have fat torque from the minute they come on boost. Leading to a wider power band.
http://autospeed.com/cms/title_Turbod-for-Fuel-Economy/A_109931/article.html

I would say turbo lag makes them more difficult to drive but to each his own. I'm not a race car drive, so such things don't really matter to me when choosing a car.

If you want something with good mpg and emissions, it's time to get yourself a new downsized turbo then isn't it.

My 05 Civic is rated for 26/35mpg and is classified as a ULEV. What downsized turbo ICE that's available in the US can provide the same emissions and fuel economy for around the same price?

 

[Topher925]

Funnily, that question was asked. While no durability testing has been done, peak cylinder pressures are held within the limits seen by a light duty diesel engine of comparable displacement. Obviously there will be concerns, but they didn't seem to expect anything which would inhibit the proposal's viability.

I think its important to keep in mind that just because something is viable, doesn't make it practical or even commercially acceptable. Viably, I could build a car that will out run and out perform a "downsized" ICE with the only emissions being 100% pure H2O. That doesn't mean its practical however. Well...not yet anyway.

 

[xxChrisxx]

It's called progress. Time will tell if what your or I say is right or wrong.

You asked for examples of downsized engines giving better mpg vs performance and I gave some. I really can't be bothered responding with increasingly long posts to a moving topic purely for a sake of argument.

Also actually read the links. The one with the torque curve shows a direct comaprison of a TSI engine (Vw direct injection) to the same TSI with a turbo.

edit: I don't mind discussing something, it's not to dismiss what you are saying. It's just the posts and number of topics being discussed are growing thick and fast. It makes having a meaningful chat about it quite difficult.

 

[jefswat]

I frankly don't have the faith to buy a turbo charged engine from any manufactures currently. Its one thing is they turbo charge a 6+L diesel engine, but its quite another to turbo a small engine. Yeah sure when everything is working great the car and engine is amazing, but if anything is out of whack it can cause big problems. NA cars are easier to trouble shoot since there is less going on. Not to mention, most car companies now like to cut corners. I don't want anyone cutting corners on a part that can shred little pieces of metal and suck them into my engine. I know a lot of mechanical engineers, and I'm afraid to touch anything they've designed. Some of the things people do I swear. I also know a significant number of structural engineers like that...

Bottom line: large displacement engine's are not very efficient in many respects. Turbo charged engines are more expensive, complex, and overall pains to work on. I would be more comfortable owning a NA for my DD, but I'd love either for a weekend car.

 

[HowlerMonkey]

The big reason you don't see bigger gains from the turbo diesels is that most are shaped like phone booths.

Put a turbodiesel in an aerodynamic sports car and watch the mileage figures go up.

 

[fredric21]

The smaller engine would have to win every time. Because the parts are smaller, raw material costs are lower. Smaller bores and strokes mean less friction and less total area for heat flux into the coolant.
The entire engine will be lighter and more responsive due to less part inertia. Higher rpm's are possible with no loss of reliability because piston speeds would be similar to the larger engine.
As an example, I have designed an engine with only two cylinders for 500cc's displacement and a theoretical 406 BHP at 15,000rpm.
I am currently assembling the prototype in my garage. It has both a supercharger and a turbo for BMEP's up to 620psia using water/methanol injection to mimic 150 octane gasoline.