Gas & diesel engines are converging

[Garak]

Originally Posted By: SteveSRT8
Our gasoline engines use a simple stainless box with copper coils inside that takes coolant before the heater core and easily produces huge volumes of perfectly heated water while cooling the engine extremely effectively during stationary ops. Very simple and highly effective.

You'd giggle at how things are opposite up here, obviously because of the climate. I can't say how it was in the States, but the Ford 7.3 Powerstroke up here would automatically go into a high idle mode if you were sitting idling for a certain period, at least in the cold. Plenty of the larger diesels have a fast idle switch.

If you go to a place called Peavey Mart up here, you would find a huge number of options for installing auxiliary heat for things like commercial vans, skid steers, backhoes, and so forth.

 

[supton]

I took my Jetta to work the other day, it was about 30f, and I took the slower back road. 42 miles and if the thermostat opened it had to be only on the last two miles, once I got onto the highway for a bit of 60mph. I should put a SG into it.

But what a range and mpg!

 

[hattaresguy]

Originally Posted By: blackman777
Mazda says their low-compression diesel is More efficient (versus their standard H.C. diesel) wwith more thorough burning of the fuel & less soot produced. They were also able to increase the redline to almost 6000 rpm, like a gasser


That's old hat Mercedes over the road diesels have been doing that for 30 years.

The problem is when you get over around 5k the ignition of the fuel starts to follow the piston so the power curve falls flat. Hence why the fuel cut off is usually just below 5k, or just over on the 90's vintage 606's, which had an extremely efficient 4 valve twin cam head design.

Some of the crazy Finish guys scream them to way over 6k but I don't think those last couple thousand RPM gains them much.

 

[NateDN10]

Originally Posted By: Shannow
Originally Posted By: NateDN10
One of the main reasons diesels typically use such high compression is for cold starts - the higher the CR, the more the temperature in the combustion chamber increases when the piston moves from BDC to TDC on the compression stroke. Mazda had to do some interesting things with injectors and valve timing to get reliable cold starting with low CR.


Nope, C.R. equals thermal efficiency...that's a diesel fundamental.

I don't disagree with you.

But in our current regulatory environment, reducing NOx emissions is very important and so lowering compression ratio is desirable, even if it lowers efficiency.

 

[Cujet]

No offense, but there is a whole bunch of speculation going on.

Rather than talk nebulous efficiency numbers, lets publish BSFC charts and operational envelopes. Then compare various technologies. We can also look a Volume specific fuel consumption and energy content of the specific fuels in question.

Today's diesel contains less energy per gallon than it did in the recent past. For that matter, so does today's gasoline.

Clearly, the older Jetta's achieved better MPG's, for example. Does this mean the new engine is less efficient? Or is the newer car larger, heavier and does it require more energy to move the air out of the way?

Older VW diesel

Newer vw diesel

 

[Cujet]

http://ecomodder.com/wiki/index.php/Brake_Specific_Fuel_Consumption_(BSFC)_Maps

A neat link that in some cases, illustrates the older vs. newer debate.

 

[Cujet]

By the way, the Lowly Lycoming aircraft engine in my Cessna will easily and readily achieve a high speed cruise, BSFC of 0.38 Lb/HP/HR or 231 g/kwh. And, that is without running lean of peak, without modern advancements, high compression pistons and so on.

The very same engine on an Experimental Velocity aircraft with dual electronic ignition, GAMI injectors, tuned exhaust and 10 to 1 pistons achieves a BSFC of 0.35 LB/HP/HR or 212 g/kwh. Not bad for 1930's technology.

Lycoming produces a FADEC version of this engine with similar results. Impressive indeed and equal to the efficiency of diesels by weight of fuel carried.

There are even some who claim to achieve as low as 0.32 LB/HP/HR, but I don't believe it.

 

[Shannow]

Originally Posted By: Cujet
No offense, but there is a whole bunch of speculation going on.

Rather than talk nebulous efficiency numbers,


The theoretical thermal efficiency limits for the operating cycles is neither nebulous, nor speculative.

It gives the upper limits to the thermal efficiency that can be obtained assuming that you get everything else right...tells you exactly how far you CAN go before engaging in speculative limits.

Yes Lycoming gets BSFC very right, and they probbly have great highway mileage but aren't that flash around town,and with catalysts and EGR.

 

[blackman777]

Originally Posted By: SteveSRT8
Just put 15 gallons of urea in my friends giant diesel pusher motorhome... IMO in cars we haven't yet found the right attributes for a diesel. When they become completely like a gasoline powered engine in all ways then we might look at one

False, false comparison. Neither the VW nor Mazda diesels use urea, so they are every bit as easy to maintain as gasoline. (Easier actually because diesels don't need to stop for fuel every 400 miles, or change oil every 7000 miles.)

As for heat: My VW diesel makes my interior like an oven in 5 minutes & forces me to turn the temperature setting down. (Yes even when I'm visiting the 0 degree temps of the cold northeast.) I'm not sure why people say diesels produce no heat? Mine produces enough it could cause heat stroke. (After all, diesels are only 45-to-50% efficient... the rest is waste heat.)

 

[blackman777]

Originally Posted By: blackman777
- SkyActive G-motor is 14:1 (highest compression for a gas engine)


I recently learned the American market only gets 13:1 because Mazda thinks Americans are too dumb to remember to use premium fuel. (sigh)

 

[440Magnum]

The diesel cycle gets its efficiency from 3 main things, IMO:

1) part of it is relatively high static CR
2) A much bigger part of it is how turbocharging can be used. With a diesel, you don't need to worry about high induction tempeatures and detonation. In fact high induction temps (within limits) are GOOD for efficiency- the heat shed by an aftercooler is wasted fuel, just like the heat shed by a radiator or exhaust. You need SOME aftercooling to allow efficiencies in other areas, but boost pressure is almost unlimited. In short, a turbo on a diesel can recover a much, much bigger fraction of waste exhaust energy than a turbo on a spark ignition engine, because a spark-ignition engine will detonate if you "work" the turbo too hard.
3) No throttle, no associated pumping losses.


As I said before, diesels on the market (in North America, for sure) in 2013 are highly compromised by emissions aftertreatment devices that waste fuel for the purpose of burning soot. Modifying injection and combustion to reduce soot coming out of the combustion chambers can help efficiency, and you could see that in the steady increase of diesel engine efficiency and reduction of smoke output from the 1960s through about 2003 or so... but AS SOON AS you start trapping soot in a filter and raising EGT's to burn it to CO2 and water, you ARE WASTING ENERGY for the sake of cleaner exhaust. Its that simple.

 

[440Magnum]

And FWIW, I think Selective Catalyst Reduction (urea injection) is an annoyance, another consumable, and another failure point, and certainly less than ideal. But I don't think its the big fuel efficiency killer that DPF is. Burning that soot DIRECTLY takes fuel. SCR with urea, or EGR, or similar technologies may indirectly hurt by requiring the engine to be run slightly off-peak efficiency, but its not the in-your-face, potato-in-the-tailpipe, run-the-EGT to the sky nonsense that DPF is.

 

[KrisZ]

Originally Posted By: blackman777
I'm not sure why people say diesels produce no heat? Mine produces enough it could cause heat stroke. (After all, diesels are only 45-to-50% efficient... the rest is waste heat.)


The reference about little heat is for idle condition, when under load, diesels have no trouble producing heat.

 

[440Magnum]

Originally Posted By: KrisZ
Originally Posted By: blackman777
I'm not sure why people say diesels produce no heat? Mine produces enough it could cause heat stroke. (After all, diesels are only 45-to-50% efficient... the rest is waste heat.)


The reference about little heat is for idle condition, when under load, diesels have no trouble producing heat.


And to be even more specific- at idle they produce a similar amount of heat as a gasoline engine at idle. However, the gasoline engine rejects a bigger percentage of the idle heat to its coolant than the diesel. Because the diesel is un-throttled, it gulps cylinders full of air even at idle, and blows a lot of the combustion heat out with the large volume of air its pumping into the exhaust. The gasoline engine has a pinhole-sized air inlet at idle and is moving a very, very small volume of fresh air through the cylinders and into the exhaust. So the heat produced conducts into the cylinder walls more than it does in a diesel.

Or to put it simply: at idle, a diesel is cooled primarily by its intake air, a gasoline engine is cooled primarily by its coolant.

 

[dareo]

4. Diesels need no specific air / fuel ratio. They only need enough fuel to actually move the pistons under the current needs. Idle is almost nothing. Extremely lean ratios gassers could never dream of are normal.

The slightest change in fueling would directly change the idle speed (or in gear cruising speed too) With a gasser it just runs richer or leaner and waits for throttle inputs and spark timing inputs.

 

[SteveSRT8]

We have a very experienced Factory Authorized upfitter that has been building our trucks since 1980. This means we still have a warranty good at any dealer just like an ordinary truck.

The reason diesels do not make enough heat for us is we need a HUGE rise in temp, going from ambient to 200 degrees or so, in a large volume of WATER. Our other PTO powered equipment simply does not provide enough work to make a diesel heat water through a heat exchanger.

There's quite a bit of calories needed to do what we do, and I have seen trucks running at 1750 rpm with two guys working simultaneously with the thermostat completely closed on a 6.0 gas motor.

We are not simply heating our toes in cold weather...

 

[rslifkin]

Originally Posted By: SteveSRT8
We have a very experienced Factory Authorized upfitter that has been building our trucks since 1980. This means we still have a warranty good at any dealer just like an ordinary truck.

The reason diesels do not make enough heat for us is we need a HUGE rise in temp, going from ambient to 200 degrees or so, in a large volume of WATER. Our other PTO powered equipment simply does not provide enough work to make a diesel heat water through a heat exchanger.

There's quite a bit of calories needed to do what we do, and I have seen trucks running at 1750 rpm with two guys working simultaneously with the thermostat completely closed on a 6.0 gas motor.

We are not simply heating our toes in cold weather...


In that case, I have to wonder if it would be more fuel efficient to use a gas or diesel fired heater to keep engine coolant temps up and only run the engine at the minimum rpm needed for extended PTO operation.

 

[SteveSRT8]

Originally Posted By: rslifkin
Originally Posted By: SteveSRT8
We have a very experienced Factory Authorized upfitter that has been building our trucks since 1980. This means we still have a warranty good at any dealer just like an ordinary truck.

The reason diesels do not make enough heat for us is we need a HUGE rise in temp, going from ambient to 200 degrees or so, in a large volume of WATER. Our other PTO powered equipment simply does not provide enough work to make a diesel heat water through a heat exchanger.

There's quite a bit of calories needed to do what we do, and I have seen trucks running at 1750 rpm with two guys working simultaneously with the thermostat completely closed on a 6.0 gas motor.

We are not simply heating our toes in cold weather...


In that case, I have to wonder if it would be more fuel efficient to use a gas or diesel fired heater to keep engine coolant temps up and only run the engine at the minimum rpm needed for extended PTO operation.


As stated in a previous post, the heater adds a whole layer of complex and finicky parts. All we use is a simple box with copper tubing in it, then run the coolant through it. I've owned the complex heated systems and they break often in the real world.

Fuel requirements are about 1-1.25 gallons per hour in stationary ops, can go to 1.5 if heavily loaded (2 guys working).

Since our oldest van was just sold with 500k miles on it it would seem that our upfitter knows what they are doing. They have real GM G team engineers on the payroll. It should also be noted that this equipment has by far the highest resale in the industry. That is real illuminating...

 

[blackman777]

Oh and also the Mazda Skyactive-G engine holds its throttle wide open during cruising. Like a diesel.

 

[SteveSRT8]

Originally Posted By: blackman777
Oh and also the Mazda Skyactive-G engine holds its throttle wide open during cruising. Like a diesel.


With the advent of cylinder deactivation the throttle programming is indeed quite bizarre. Mazda is not the only mfgr to hold the throttle open under certain operating conditions.

You should see what our 6 liter gas engines do with the throttle plate in our service vans when they are turning 1300 rpm at 60 mph and running on 4 cylinders!