Maximum pressure in a diesel engine

[Space car]

What is the maximum pressure that a person should design for in a diesel engine cycle (normal operation)? If the answer is different according to size or type of service, All kinds are of interest Is 22 MPa (3200 psi) too high? Too low? References are appreciated. I thought I remembered an engine designed to 25 MPa peak.

 

[TugboatEng]

Are you planning to build an emissions compliant engine as that will very much dictate your peak pressures due to NOx emissions?

 

[Space car]

Thanks, Tugboad, that is a very helpful question. As I see it, high power and high efficiency mean high pressure, and with that comes NOx. A cargo ship engine running on ammonia might be an exception to the rule, but today I am just looking at diesel fuel. I am thinking of large engines that run at nearly constant power. I have been assuming that in this case aftertreatment is a practical choice, so--up the temperature and pressure for best efficiency and let someone else design the aftertreatment system. If you see that as a reasonable position, then I am excited to hear what a large engine guy (I guess you are) can tell me.

 

[TugboatEng]

It is correct that after treatment allows the engines to operate at higher peak pressures and passes the burden on to the SCR. I operate many Caterpillar 3500 series engines and the Tier 3 (all emissions management done in cylinder). Operate at lower horsepower and lower fuel efficiency than Tier 4 which is the same engine with different programming and SCR.

Ammonia engines will require SCR as NOx will be the exhaust.

 

[gruntguru]

Tugboat, I think the ideal products of ammonia-air combustion are H20 and N2. NOX will be an undesirable (albeit relatively high) byproduct as in any combustion process.

je suis charlie

 

[Lou Scannon]

Some combustion processes have inherently low NOx, e.g. lean HCCI, but so far nothing with low engine out NOx is still commercially competitive in heavily regulated markets, as far as I know.
Lean H2 has low engine out NOx, but so far this is just a niche and a hope for the future.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[Lou Scannon]

Back to the OP, the peak pressure depends a lot on the base engine capability, and the life expectancy. 220 bar is near the current limit for large off-highway diesel engines, that have TBO in the 20-30,000 hour range, and total life expectancies north of 80,000hr.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[itsmoked]

Tug; Are those definitions of Tier 3 and 4 kinda universal? i.e. would they stand for, say, buses and harvesters?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Space car]

Hey, Lou, thanks for the note and the numbers. If you get back to me on this, I wonder if you have any references I could look up? /Ernie

 

[TugboatEng]

Itsmoked, it's based in the USA on per cylinder displacement. The world has comparable tiers, IMO (international maritime organization) is starting to enforce Tier 3 but US EPA requires Tier 4. It's very complicated for those that work offshore. I'm currently working to convert my fleet to Tier 3 though I think we should be shooting for tier 4 with frustratingly little support.

 

[Lou Scannon]

Engine builders are pretty secretive about internal data such as peak cylinder pressure so I don't know any references on the internet to quote.
However, you might find research papers with published pressure vs crank angle curves that would give you a hint. But typically these research papers do not represent commercially available engines.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[catserveng]

Keith,

Good overview of EPA tiers as applied to larger diesel engines here,

https://dieselnet.com/standards/us/nonroad.php

To the OP, have you looked at the Southwest Research site? They have done a lot of both independent and and collaborative studies and research with most all the North American diesel engine manufacturers and distributors. And also with several smaller companies and regulatory agencies on diesel engine performance and emissions research. This podcast talks about a lot of the issues touched here, and maybe you will find it helpful,

https://www.swri.org/podcast/ep20

When I was with CAT we did a number of programs where we pushed industrial engine cylinder pressure quite high, if power and fuel economy were our only targets, we could make pretty significant improvements, we did end up with "high performance" engine ratings that packed a lot of horsepower in smaller displacement units. But having to meet both emissions standards and customer expectations for service life required scaling back cylinders pressures.

Also the regulatory agencies weren't always helpful in the true pursuit of better engines, for a number of years we had ratings that were a compromise between good power and fuel consumption rates and lower emissions. Sometimes things got done to lower NOx output that had significant detrimental affects of fuel consumption, particulate and CO and CO2 emissions. Improvements in aftertreatment systems has helped that some, but finding getting and keeping an aftertreatment system working well and keeping an engine in compliance, especially engines with cyclic loading conditions, can be quite a challenge.

Hope that helps, MikeL.

 

[Space car]

Thanks, guys,
Keith, I listened to the aftertreatment podcast at SWRI, sent a follow-up message to Chris Sharp who is in charge of their work.