Would this be a good engine design?


#1

Would this be a good engine design (I’m not a marine engineer, but I have knowledge from hanging around with my Dad, a former shipmaster, now a marine surveyor, and his colleagues. Feel free to call me crazy if that’s what my idea is)?

After the second stroke of a two stroke diesel, spray water into the cylinder. This will accomplish two things: engine cooling and use the heat that would normally be wasted to provide an extra power stroke. And the steam exhaust will provide extra boost to the turbocharger.

The water needed could come from the reverse osmosis system, so minimal weight would have to be added, just a few extra pipes. The engine would need to retrofitted w/ fuel injectors and a timing system, though.

Less fuel will need to be used, meaning less shipping costs. And the engine will last longer.

I got my idea from this article: http://en.wikipedia.org/wiki/Crower_six_stroke

I’m not sure whether I should pursue a career on deck, or in the engine room. I only have second-hand knowledge of both, so could you guys enlighten me on what a career in marine engineering is like?


#2

I don’t think this would work well. As you cool the exhaust it would become more dense and therefore you wouldn’t have as much flow over the turbo. Who knows though, it might be offset by the steam expansion. You’d have to worry too much about water droplets hitting the turbo blades though. The piston and cylinder jacket already recieve enough cooling that injecting water into the cylinder isn’t necessary. Internal combustion engines have been around for awhile so chances are someone thought of this awhile ago and it hasn’t proven to be cost efficient.


#3

If you are considering a career in the engine department this will be a good way to start your education.

A modern slow-speed 2-stroke marine diesel rejects around 5 to 8 percent of the energy available in the fuel through jacket water cooling. That means if a unit of fuel contains 100 BTUs, somewhere between 5 and 8 of those BTUs will be removed from the cylinder by the cooling water.

Now, your assignment, should you choose to accept it, is to determine the number of BTUs required to produce a volume of steam that will fill the cylinder at a pressure equal to the firing pressure average (you can use BMEP since that figure is widely published for any given engine) and then figure out if there is (1): enough heat to evaporate the required amount of water, and (2): if cooling that cylinder through the “steampower” stroke will still keep it hot enough to prevent condensation in the cylinder which will kill the engine in very short order.

I think you will find that there really is no free lunch in the energy conversion business, and that is the underlying business of a marine engineer. It is also what makes this job so fascinating, once you get beyond the mechanics of keeping the plant online it becomes art and then it is really fun.

Look up: Large 2-stroke marine engine heat balance
Saturated steam tables (red flag word there)
Waste heat recovery
Combined cycle powerplants

Good luck and have fun


#4

[quote=Steamer;21459]If you are considering a career in the engine department this will be a good way to start your education.

A modern slow-speed 2-stroke marine diesel rejects around 5 to 8 percent of the energy available in the fuel through jacket water cooling. That means if a unit of fuel contains 100 BTUs, somewhere between 5 and 8 of those BTUs will be removed from the cylinder by the cooling water.

Now, your assignment, should you choose to accept it, is to determine the number of BTUs required to produce a volume of steam that will fill the cylinder at a pressure equal to the firing pressure average (you can use BMEP since that figure is widely published for any given engine) and then figure out if there is (1): enough heat to evaporate the required amount of water, and (2): if cooling that cylinder through the “steampower” stroke will still keep it hot enough to prevent condensation in the cylinder which will kill the engine in very short order.

I think you will find that there really is no free lunch in the energy conversion business, and that is the underlying business of a marine engineer. It is also what makes this job so fascinating, once you get beyond the mechanics of keeping the plant online it becomes art and then it is really fun.

Look up: Large 2-stroke marine engine heat balance
Saturated steam tables (red flag word there)
Waste heat recovery
Combined cycle powerplants

Good luck and have fun[/quote]

I wish I knew enough physics to answer these questions. I’m only in community college, and the physics classes are closed.


#5

Call me old-fashioned.

I’ve spent forty years trying to keep water OUT of the engines. I’m not saying there isn’t a way to do it, but I’m not smart enough to envision it.

Problems with corrosion, friction, heat buildup and lubrication (or lack thereof) are just some of the problems that come to mind.

And I’m just a deck guy. I don’t know “Come here” from “Sic’em” about engines. Changing fluids and filters is about the limit of my mechanical knowledge but I’m sure there are some wrench benders on here that can elaborate.

Nemo


#6

[quote=Steamer;21459]

I think you will find that there really is no free lunch in the energy conversion business,[/quote]

Ha! Yes, I’ll put my money there as well.

From the wheel house perspective what we are faced with today with a slow speed engine is maintenance issues related to incomplete combustion as a result of slow speed steaming to save fuel. This problem is likely going to get more acute in the future as the price of fuel continues to increase. I want to slow down for a timed arrival, the chief wants to run at 85% load. I can’t run donuts like a few years back because the guys in the office with the distance / fuel burned spread sheets are breathing down my neck.


#7

The physics are not much beyond high school level and the thermodynamics are basement level stuff. Google the topics I listed and have a read. Also, the engine manufacturers have published a ton of technical papers on how they address the problems involved in using water to reduce NOx production and how they manage cylinder conditions in large 2-stroke engines. Wartsila has a whole library online.

Don’t give up because a class is full … develop a healthy case of intellectual curiosity, blend that with some research skills and you will be way ahead of the game.

Good luck


#8

[quote=Steamer;21459]If you are considering a career in the engine department this will be a good way to start your education.

A modern slow-speed 2-stroke marine diesel rejects around 5 to 8 percent of the energy available in the fuel through jacket water cooling. That means if a unit of fuel contains 100 BTUs, somewhere between 5 and 8 of those BTUs will be removed from the cylinder by the cooling water.

Now, your assignment, should you choose to accept it, is to determine the number of BTUs required to produce a volume of steam that will fill the cylinder at a pressure equal to the firing pressure average (you can use BMEP since that figure is widely published for any given engine) and then figure out if there is (1): enough heat to evaporate the required amount of water, and (2): if cooling that cylinder through the “steampower” stroke will still keep it hot enough to prevent condensation in the cylinder which will kill the engine in very short order.

I think you will find that there really is no free lunch in the energy conversion business, and that is the underlying business of a marine engineer. It is also what makes this job so fascinating, once you get beyond the mechanics of keeping the plant online it becomes art and then it is really fun.

Look up: Large 2-stroke marine engine heat balance
Saturated steam tables (red flag word there)
Waste heat recovery
Combined cycle powerplants

Good luck and have fun[/quote]

Well, here’s my attempt:

Assuming a BMEP of 10 bar, a cylinder size of 100 mL, and an operating temperature of 110 degC.

We need to vaporize enough water to fill a 100 mL cyinder at 10 bar at 110 degC.

Now, according to the ideal gas eqn, the number of moles needed to fill 100 mL at 10 bar, at an operating temp of 110 degC is (values will be converted to atmospheres, liters, and Kelvins):

n=PV/TR
n=(9.87 atm * .1 L)/(.0821 L-atm/mol-degK * 383K)
n=0.0314 mol

So we need enough heat to vaporize 0.0314 mols of water, and get it to a temperature of 110 degC. The molar mass of water is 18.015 g/mol, so we need .566 g of water

The specific heat of water is 4.184 J/g/degC. Assuming the water is at 0C, we need to add

4.184 J/g/degC * .566 g * 100 degC= 23.68 J of heat

Then we need to add 2.257 J/g/degC to vaporize it, or 0.1277 J of heat.

Then we need to add more heat to bring it up to 110 degC, or

2.080 J/g/degC * .566 g * 10 degC = 11.77 J

Total heat needed is 35.58 J

And I did figure out that since 100 mL of steam can be produced from .566 mL of water, the water will expand 176.68 times in this enviroment.

Now, I’m stuck at answering the other questions, and I doubt this answer is correct.


#9

[quote=Kennebec Captain;21596]Ha! Yes, I’ll put my money there as well.

From the wheel house perspective what we are faced with today with a slow speed engine is maintenance issues related to incomplete combustion as a result of slow speed steaming to save fuel. This problem is likely going to get more acute in the future as the price of fuel continues to increase. I want to slow down for a timed arrival, the chief wants to run at 85% load. I can’t run donuts like a few years back because the guys in the office with the distance / fuel burned spread sheets are breathing down my neck.[/quote]

My last vsl with 75.000 hp:
I had 5 day discussion with my c/e to reduce for only 2 revs. I was suffering for next two weeks for his low voice grumbling. He even wanted to complain to company about my command… I had it my way, on the end. (he had a choice: my way or the gangway).
I reduced revs, and he was finnaly complaining about my skills to his 1st engineer, as compromising solution…

After a month I signed off, he stayed o/b, and company sent orders to reduce to full manouvering speed, with blowers running, etc…

I just wish I could see his face on receipt of that order!
Feel sorry for my releiver captain, though.


#10

[QUOTE=Protoman2050;21626]Well, here’s my attempt:

Assuming a BMEP of 10 bar, a cylinder size of 100 mL, and an operating temperature of 110 degC.

We need to vaporize enough water to fill a 100 mL cyinder at 10 bar at 110 degC.

Now, according to the ideal gas eqn, the number of moles needed to fill 100 mL at 10 bar, at an operating temp of 110 degC is (values will be converted to atmospheres, liters, and Kelvins):

n=PV/TR
n=(9.87 atm * .1 L)/(.0821 L-atm/mol-degK * 383K)
n=0.0314 mol

So we need enough heat to vaporize 0.0314 mols of water, and get it to a temperature of 110 degC. The molar mass of water is 18.015 g/mol, so we need .566 g of water

The specific heat of water is 4.184 J/g/degC. Assuming the water is at 0C, we need to add

4.184 J/g/degC * .566 g * 100 degC= 23.68 J of heat

Then we need to add 2.257 J/g/degC to vaporize it, or 0.1277 J of heat.

Then we need to add more heat to bring it up to 110 degC, or

2.080 J/g/degC * .566 g * 10 degC = 11.77 J

Total heat needed is 35.58 J

And I did figure out that since 100 mL of steam can be produced from .566 mL of water, the water will expand 176.68 times in this enviroment.

Now, I’m stuck at answering the other questions, and I doubt this answer is correct.[/QUOTE]

keep working on it, you never know what you can come up with, might lead you into a new engine design, best of luck:)


#11

Interesting concept. I would more think of adapting a 4 stroke engine to a combined cycle stroke with the 2nd rotation being the steam stroke. One big problem is the loss of heat in the cylinder due to losing thermal energy to latent heat of vaporization of the water. You will also have energy loss on the second stroke due to compressing the combustion gasses before the water is sprayed in. You will want to spray the water in at TDC.
Another way of doing the thermal reclaim is to use a gas turbine as your initial combustion process with a steam generator on the exhaust of the gas turbine. The steam generator would spin another turbine or turbines, one for propulsion the other for electrical generation.
Constant combustion is a far easier method to achieve complete combustion over a wide range of power outputs. A gas turbine is a constant combustion device. A boiler is a constant combustion device. Diesel engines are intermittent combustion devices.
Gas turbines with thermal reclaim at shore side power plants have have achieved 80% efficiency of conversion to electrical power.