BSFC turbocharged vehicles
 

I was wondering n/a vehicles runs best at 80 percent load at around maybe 2000-2500 rpm. How about turbocharged gasoline engines? What if lets say at low RPM boost kicks in i believe entering into boost will require a rich mixture so will probably kill effeciency? so what is the "general rule" on these engines? and how about diesel? VGT engines turbo kicks in so early and from what i understand diesel is effecient when in boost? is this correct?

I think turbocharged vehicles vary much much more and you would have to study the stock tune to get a feel for this.

Good rule of thumb is the highest load where it's still stoichiometric is the most efficient load. Some turbo engines can stay stoichiometric under boost (newer ones), while others run rich quickly. You can get much more mpg by leaning out the fueling under boost.

On a diesel it's hard to tell because combustion efficiency is much more variable.

With VVT it is possible to trade torque for efficiency. You can delay the intake valve to get "simulate Atkinson cycle", which decreases VE and allows you to open the throttle fully while not inducting as much air. I don't think this is a common setting since I imagine response would typically be prioritized, but I have no idea.

I see so it will vary model to model thanks

oh and im reading lots of articles mentioning how turbocharged engines are "effecient" due to the volumetric effeciency i think? is this true since there is a posibility of a more rich mixture?

Volumetric efficiency increases the more air you can get in to the cylinder, so yes, forced induction increases volumetric efficiency.
Unfortunately, to keep combustion chamber temps down and prevent detonation, gasoline engines usually pump extra fuel in that goes unburnt. The only real way (that I am aware of) to prevent the need for this is to inject the fuel immediately before it's to be ignited (direct injection). So, yes, some modern engines can be turbocharged and have higher compression ratios and are thus can be more efficient.

Diesels run more efficiently under boost. The higher air mass in the engine absorbs more combustion heat and thus keeps it from being absorbed by the cylinder and combustion chamber. The extra heat energy absorbed by the air can then be extracted in the power stroke.

Keep in mind that the benefit from this is a diminishing return and beyond a certain point frictional bearing losses from the increased pressure will overwhelm any gains.

I see so it still highly depends on lots of factors then

MOST turbocharged vehicles run slightly rich under boost, even if the ecu doesnt "see" it that way, its just a way to keep the combustion process happy with added air and temperature. and most factory cars, like my cruze 1.4, with tiny hairdryer sized turbos, are almost always under boost. my car is at 0 psi at 55 ish(which is still technically in boost) and it just goes up with more speed. not entirely an efficient design

When sizing gasoline fuel injectors you figure 0.6 pounds per horsepower per hour.
For N/A it's 0.5 pounds per hp per hour.
Turbo rotory engines can be around 0.7 pounds, well you know.

I was wondering that myself. Got a new Fiesta ST. Right now, calculated ~30-31 mpg average, mostly highway. been cold, I mean it is winter! I bet I can get it up in the mid 30's. But its of course not the best choice for mileage.

Once the turbo is building up pressure, as a rule of thumb, a smaller engine that would otherwise be deemed underpowered and need to rev up higher to provide power and torque figures similar to a higher-displacement one can become more efficient. Now due to the widespread of direct injection, leaner burn can be implemented to go even further on fuel savings even though it might lead to an increase in nitrogen oxides (NOx) formation, which had been one of the Achilles' heels of Diesel engines. Cooling the air intake charge through a so-called intercooler or some water and alcohol injection is an effective way to deal with the NOx issue, and also to prevent knocks that would happen in a port-injected or a carburettor-fed turbocharged engine operating with a lean mixture at a high compression.

Modern turbocharged engines do not differ that much from naturally aspirated engines. There is not that much need for rich mixtures anymore. VW's latest engine 1.5 TSI (EA211 Evo) doesn’t need rich mixture at all. It operates at stoichiometric conditions across the entire engine map. Ford’s 1.0 Ecoboost, which has been around for some time already, uses just a bit enrichment at highest load when revs are 3600 rpm or more. 1.0 Ecoboost actually goes slightly lean when pushed hard at low revs.
I don’t like general rules because there are so many different technologies on the market. Maybe one could say, that turbocharged engine have their most efficient point at slightly lower load point than n/a engines.

That doesn't explain why it's so freaking hard to match NEDC in a baby turbo and so freaking easy in a NA engine.

I would say that all manufactures have learned to optimize their cars for NEDC test. Every new model has an unrealistic NEDC ratings. N/A engines are no different in this sense.

What makes you think that N/A engines don't have unrealistic NEDC ratings?

my turbo-celica utilizes a twin-scroll turbo, it spun up pretty quick.

If drove with DWL, it seemed to make up for my quick accelerations, MPG-wise. At least a bit.

:/ dunno then how much i'd get out of it if I really tried to hypermile it

Baby turbo engines have been built from the ground up to beat the NEDC test. Now that NEDC is being replaced with RDE there's a big scramble on to increase engine capacities. NA engines might be optimised for NEDC, but the scope of what can be done is far more limited.

I have/ have had ~10 cars over the last 3-4 years. 2014 Renault Kangoo 1.6NA, 300+ kg of cargo, roof rack, 600kg of trailer, and only on the very worst traffic days would it not match NEDC, but that was only ever by 0.1-0.3L. Without the trailer it would always hit NEDC within 2km in the morning and I'd pull up on a few occasions with the SG reading 100% over NEDC. I wonder what it would have done empty and without the roof rack?

Now the Kangoo was pretty much designed from the factory to be 100% EOC ready, so that's what I did (a lot), but I rarely EOC'd with the trailer as it would cruise pretty close to BSFC. In short even with a tiny 1.6 an extra ~1000kg, extra drag from a tall trailer and an extra set of wheels, NEDC was still easy to beat.

If Renault were trying to be unrealistic with the Kangoo they were doing a very poor job of it.

My baby turbo Fiat Twinair is only driven in pretty much ideal conditions (country trips on weekends) and has yet to match NEDC. EOC and P&G don't work as there's too much enrichment when getting up to speed.

My Renault Trafic 1.6 DCi is only new, but only just hovering around NEDC being driven on the same routes as the Kangoo. It has no roof rack and is currently carrying less than the Kangoo did, but there's no way I'd be beating NEDC with the trailer in tow.

With both of these baby turbos you really have to granny drive them on acceleration (NEDC style) to get good figures, suggesting they both do very early fuel enrichment. The NA engines are more fun because you can stomp on them a bit without an economy penalty. My average speed is 26km/h for the Renaults so it's a match for the NEDC 'city' figure. 100% of people with baby turbos including BMW's 1.5 triple seem to have the same experience.

Would substituting some of the fuel injected with water produce the same effect as over fueling?

If so how much should the ecu be tuned down and the water added? And if water can be substituted for the fuel is it wise to up the boost?

That Kangoo engine is an old engine from the time, when cycle optimization was not at the same level where it is now. If you take some more modern N/A engines, they are right there at the same level as turbocharged engines.

Your Fiat is notorious for delivering not so good real world consumption. It uses a lot enrichment. Some more advanced small turbocharged engines need very little enrichment or don't need it at all. For example small turbocharged engines from VW, PSA and Toyota are very efficient. Of course it's their NEDC ratings are unrealistic, but also new N/A engines are just as cycle optimized.

Downsized engines not going anywhere. Only small diesels have problems with their NOx emissions. The miller cycle has increased the size of few engines, but at the same time we have much more engines which are getting smaller.

Only if you can get the water to burn...

I ran my Volkswagen Passat 1.8 liter turbocharged engine really lean on the highway by using some diodes to fool the car into thinking it was at a normal AFR. I was able to get up to around 48 MPG in that car combined with some other mods like a front belly pan, more air pressure in tires, shaved antenna and a grille block. From the factory it got 29 MPG highway.

The diodes were to fool the ECU into thinking the car was getting less boost than it actually was, I used the wrong diode apparently and it kept it pretty lean.

Surprisingly, the engine is fine, the turbo is what blew up. But only because I forgot to put coolant in the radiator when it froze and the water never circulated into the turbo. Oh, and the fact it had the wastegate welded shut and no boost controller probably had something to do with it also.

What year was your passat? And do they have wideband o2 sensors or narrowmand?

I have the 1.8t 2011. Cruising at 80 kph I got 46 mpg.

BMW's 1.5 is more economical the otherwise identical 1.2.

VW Golf is dropping the 1.4 in favor of a more economical 1.5.

1.5's in this segment aren't what I'd call downsized, but the smaller engines are being dropped. If going smaller was the right way to get, the new engine would be a 1.3.

It will be interesting to see what come out of RDE.

Sounds like there is a sweet spot..

Data sheet from Mini's web site says, that the 1.2 liter engine has lower compression ratio and it reaches peak torque at higher revs then the bigger 1.5. Bore/stroke ratio is also different. BMW has replaced the old 4-cyliner 1.4-1.6 Prince engines with 3-cylinder 1.2-1.5 engines. This is downsizing.

VW's 1.4 TSI liter will be replaced by 1.5 liter unit and there are two reasons for the increase in size. The new engine uses miller cycle, which makes the intake event shorter. Bigger displacement compensates this. The bigger 1.5 liter unit also fits perfectly to tax limits in China. At the same time VW is making their highly efficient 1.0 liter unit much more popular. It will replace old 1.0, 1.2 and 1,6 liter engines. The 1.0 unit is not going be dropped. Quite the contrary, the 1.0 unit is getting much more popular.

At least here in Brazil the 1.0TSI already replaced the 1.6L naturally-aspirated in the Golf, but in lower-end models those ancient concerns about the impact of turbocharging in the fuel-efficiency and durability of the engines is still widespread, and the lack of suitable CNG conversion kits for direct-injection engines still leading the 1.6L to be prefered by some operators.

The age of engine downsizing is over, says Volkswagen

It sounded like they could not bothered to solve the issues...