Turbocharging a diesel engine?

Fred, you are wrong about Yanmar diesels. I have first hand experience with a six cylinder Yanmar turbo diesel in a jetboat on Sydney harbour about 10 years ago. I want to say the engine was rated at 315hp, but memory doesn't serve me that well.
This engine got pounded mercilessly seven days a week, on a heavily loaded boat (26 passengers in a 26ft aluminium hull). It spent lots of time at full throttle and lugging to get an overloaded boat up on the plane. The drivers were also not very forgiving....
Anyway, this engine went well past 3000 hours with ancillaries and actual installation issues being the only problems.
So, in my experience, the Yanmars are tough as nails and make the power rating they are said to and will deliver it continuously.
As for turbos, they need to be matched to where you want peak torque/rpm. My petrol Volvo has max boost by 2500 rpm and drives like a large six cylinder car, with all that midrange torque.
A turbocharged engine that is not in boost isn't unloaded, it's still doing a fair bit of work, it's just not at maximum load. I wouldn't have an issue running a turbocharged diesel just off boost.

 

Gentlemen:


Although this does not really help our original poster and his question, I do believe that it is generally accepted that the BSFC of a turbo charged diesel is better than it's non- turbo charged counterpart. In fact, I believe most fuel consumption graphs published by the various manufacturers, and then submitted to the EPA or other air emission entity for emission compliance would also bare this out.

I don't think the BSFC difference is enormous, but is in the 7-10% range average, meaning that it takes about 7-10% less, fuel to make the same amount of HP hours using turbocharging vs non-turbocharging, all else being equal from an engineering standpoint. Remember, I am not talking power density (that's a given) I am talking BSFC.


With that said, I do have a question that in the past I have not been able to get a universal answer on. Maybe it will come here?

So here goes:


Why, or what exactly is taking place inside the engine to make the engine produce the same HP on less fuel? Really simple question when you think about it, but I am wondering if there is a simple answer.

Cheers and Happy New Year to All.

Marine Nut

 

One help is the inlet stroke becomes a power stroke ( not always but generally)
There is more oxygen for the given space.
The air is hotter than atmospheric yet under pressure to make up for that
More tubulence in the combustion chamber for better mixing
Induction design and valve timing less of an issue as air supplied under pressure hence any ram effect at peak torque (assuming that was how it was designed) will be leveled out and raised.
Same torque from a smaller displacement engine means less parasitic drag
Engine can also have less ring tension ( less drag) as the combustion pressure will be higher.
( always notice your turbo engine has very dirty oil....bigger ring end gaps as well)

 

Don't confuse oil colour with level of dirtyness. Oil can colour for many different reasons including heat.

-Tom

 

The turbo is blowing air out of the cylinder during the overlap period , so the charge air is scavenged better = more oxygen , so a better more efficient burn.

Just look at the monstrous fuel burn when the engine folks were forced use Exhaust Gas Recirculation to appease the Air Police.

With 20-25% returned exhaust (2004 standards) the fuel consumption could double!!

When they went higher in 08 the engine users revolted and began purchasing 98 -2003 engines and rebuilding them.

FF

 

Hey guys I'm sold on turbocharging - not problem and if I intended on running this boat (32 Nordic) at 50-85% load I'd not be concerned at all. It's the 30-40% loading I'm worrying about. Someone said (don't recall who) that the after cooled diesel run w light loads will run too cold in the combustion chamber not burning off the bad stuff, sooting up and sticking the rings ect. One guy even said I could even experience a broken crankshaft. I want to cruise 2 or 3000 miles a year at 7 knots (35% load est) w the Nordic Tug. What's my chances of being extremely sorry I bought the boat.

 

I'd say about 40%, but it's only a guess.

-Tom

 

Marine nut,
"what exactly is taking place inside the engine to make the engine produce the same HP on less fuel"...not quite a true statement....turbo on/turbo off at the SAME revs, will use more fuel, but more hp will result?

...with the case of constant speed and constant engine RPM, load decreases significantly, it is this that shows as fuel saving, as the cylinder is being forced to run.

the turbo simply works the same way that a supercharger works (air input side anyhow), in that it delivers to the combustion cylinder a charged input of air (and air contains oxygen, which is burned up in the combustion cycle, same as on cold nights the air is more dense, in reality the oxygen is more dense, so the combustion is fiercer)...remember that a diesel is an air engine, it has NO throttle...only an injection of fuel.

...another finer point is that the compression of the piston down stroke is effectively assisted by the pressure of the induction air being forced into the cylinder compression space.

 

LL,
"the piston down stroke is effectively assisted by the pressure of the induction air being forced into the cylinder compression space."
Not likely in my opinion. I'm sure the vacuum is reduced but it's hard to imagine the air rushing in so fast it builds pressure ...of course pressure is relative and many things that seeeeem impossible in fact DO happen.
In the turbocharged engine the the exhaust part of the turbo drive's the intake part. Is there a range or a point where the the intake side starts driving the exhaust side? I would think not. 100% of the air coming in is going out but the exhaust is being driven by combustion forces so it would seem to me that as long as the engine is running there would be at least some power applied to the intake side from the exhaust. Assume a positively loaded crankshaft.
The reason I'm asking is that I've heard people say stuff like "when boost starts". I suspect it's always there. What think?

 

Hi Easy Rider,
Google "tractor pull" I think you will find information about compounded turbo's and blowers that are used to build pretty high pressures on the intake side. If you don't find much, I have a book that I can pull some information and numbers from (might be a little outdated) that will possibley help you out.

The only thing I remember that might apply to your question of operating at low power for long periods of time, is I had once ask a mechanic about using one of my Cummins engines in a method that it would hardly ever operate beyond 1000 rpm, his answer was basically "different speeds and loading at those speeds are a key to keeping wear points of moving parts spread over the maxium area of their exposed surfaces". Harmonics of one speed will cause quicker wear at a smaller area, right or wrong, it sounded logical.

Ron

 

...running the new high pressure electronic controlled injector diesels at low speed should not have the same effects that the old injector pump/injector types had. There was a glazing effect from too much fuel that no longer exists.....

"another finer point is that the compression of the piston down stroke"..was the quote, you conveniently left off the finer point, but it does exist....

 

ER,

I think you would be surprised by the dynamic air flow created by turbo charging. It likely accounts for some of the efficiency gain. Depending on level of boost, air really is being hugely assisted into the compression chamber and, depending on valve timing, "overlap", RPM and a host of other variables, helping to scavenge the chamber "clean" on the exhaust cycle as well. It is a very complex and multi-facetted process that doesn't always take well to intuition or generalizations. It is a wonderfully simple application of technology though and, if used correctly, of huge benefit.

-Tom

 

Some confusion in this thread. The turbine section of the turbo drives the compressor side to create positive boost pressure on the air intake. Not the other way around. So in all but the most specialized applications this means that turbine creates a lot of back pressure in the exhaust. This back pressure in the exhaust manifold will be higher than the boost pressure. Because of this there is no tendency for the compressed intake air to scavenge out the exhaust gas (unlike a supercharger). This is also why the intake stroke can not become a power stroke. The pressure of the intake air will not be high enough to overcome the even higher exhaust back-pressure of the exhaust stroke of the opposing piston. The sucking action of the pistons will draw the compressed air in but the charge will have slightly more exhaust gas contamination than a naturally aspirated engine due to increased exhaust manifold back pressure. The increased charge density of the compressed air will more than overcome any drawbacks of the slightly increased charge contamination.

 

There certainly is confusion on this thread about turbocharging.

It's too bad.

I'm out.

-Tom

 

Sounds like your cam lobes might be a little worn flat ???????

Ron