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natural gas/diesel dual fuel engine validation

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Old   October 16, 2017, 15:51
Default natural gas/diesel dual fuel engine validation
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Hello,

I'm doing some validation cases for natural gas/diesel dual-fuel combustion. When I compare CONVERGE in-cylinder pressure prediction with my experimental data, everything is good regarding the SOC, combustion phasing, peak pressure except expansion stroke pressure. I really don't know why CONVERGE over-predicts the expansion pressure? Also, this over-prediction is more pronounced for very advanced diesel injection timing (e.g. 46 BTDC) compared to late injection timing (e.g. 26 BTDC).

I'm using the methane/n-heptane mechanism from the SAGE dual-fuel example file.

Last edited by amin_u50; October 19, 2017 at 12:05.
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Old   November 6, 2017, 03:26
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Wow, that sounds really good. i did read some news about gas diesel dual fuel engine but I knew only a few about it.
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Old   November 6, 2017, 03:40
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Diesel is super expensive now i think. and that is the reason why we need dual fuel. I have a diesel generator which is used for supplying standby power for my house and it does burn so much fuel every time I try to run it. And if there is a kind of generator which could use dual fuel to run, then I wil be very happy.

I got a truck which also burn diesel. It use the yuchai Yc4108 series engine. But it still cost a lot of momey to supply it.

I learn from the news about dual fuel that it is better than diesel or gas.

When operating at part load, dual-fuel engines can suffer from excessive incomplete combustion of the natural gas, which results in increased tailpipe emissions of methane and other pollutants. Another problem with natural gas is that chemical reactivity of the “pipeline quality” fuel can vary greatly from day to day, or region to region, depending on the percentage of ethane and propane in the natural gas.
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Old   December 12, 2017, 07:34
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Hey,

Did you compare also the heat release rate and temperature? Do they match with experimental ones?

Sometimes pressure curve is not enough for validating a certain case.

Secondary, consider also that generally experimental data are an averaged result from several engine cycles, then your simulation of single combustion won't match exactly with experiments. Take care about the fact that specially at low-loads operating conditions COV of Dual fuel can be high then "distance" between experimental and one-shot simulation can be high as well.
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Old   December 12, 2017, 11:37
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Quote:
Originally Posted by TWIN View Post
Hey,

Did you compare also the heat release rate and temperature? Do they match with experimental ones?

Sometimes pressure curve is not enough for validating a certain case.

Secondary, consider also that generally experimental data are an averaged result from several engine cycles, then your simulation of single combustion won't match exactly with experiments. Take care about the fact that specially at low-loads operating conditions COV of Dual fuel can be high then "distance" between experimental and one-shot simulation can be high as well.
You are completely right. Thank you for the comment.
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Old   December 12, 2017, 18:41
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Andrea pointed out several important points that you should look at for early injection dual fuel engines. Couple of additional pointers:

1. You should check to see if you are matching intake flow rates well. We would recommend the intake mass flow rates to match within 2% at IVC

2. Are you modeling the correct composition of NG so that your fuel heat value (LHV) is correct? CONVERGE allows you to correct for the LHV of your surrogate to match that of the actual fuel used

3. Plot the CONVERGE predictions against actual cycle data and not averaged mean cycle data. You have to look at the CCV of the measured cylinder pressure and see if the predictions are within these variations.

4. If you are at a larger NG substitution ratio and injecting a very small amount of diesel very early, the possible uncertainties on wall temperatures and the amount of diesel injected can be quite critical.

Read this paper by GE and Convergent Science on this topic: "Multidimensional Modeling and Validation of Dual-Fuel Combustion in a Large Bore Medium Speed Diesel Engine", ASME ICEF2015-1077

If nothing works, please email you case setup to support@convergecfd.com

Thanks,
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Old   December 13, 2017, 16:26
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Quote:
Originally Posted by SamWijey View Post
Andrea pointed out several important points that you should look at for early injection dual fuel engines. Couple of additional pointers:

1. You should check to see if you are matching intake flow rates well. We would recommend the intake mass flow rates to match within 2% at IVC

2. Are you modeling the correct composition of NG so that your fuel heat value (LHV) is correct? CONVERGE allows you to correct for the LHV of your surrogate to match that of the actual fuel used

3. Plot the CONVERGE predictions against actual cycle data and not averaged mean cycle data. You have to look at the CCV of the measured cylinder pressure and see if the predictions are within these variations.

4. If you are at a larger NG substitution ratio and injecting a very small amount of diesel very early, the possible uncertainties on wall temperatures and the amount of diesel injected can be quite critical.

Read this paper by GE and Convergent Science on this topic: "Multidimensional Modeling and Validation of Dual-Fuel Combustion in a Large Bore Medium Speed Diesel Engine", ASME ICEF2015-1077

If nothing works, please email you case setup to support@convergecfd.com

Thanks,
Thank you for your good answer. I read this paper before and you found that wall temperature and diesel quantity are critical because combustion starts from the outer part of combustion chamber. That's absolutely correct.

My question is why did you examine only diesel quantity and wall temperature? Maybe natural gas mass flow affects the combustion phasing as well. How did you measure the sensitivity of natural gas mass flow on combustion? Does it affect too much if 20% more (or less) natural gas is used?
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Old   December 13, 2017, 17:49
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The uncertainties checked for in the paper was determined by the industrial partner of the paper. They decided based on their experiments, that these uncertainties were possible. The NG mass flow rate was accurately measured at the inflow and hence the uncertainty of that was small. Since the same injector was used to inject 100% diesel (0% NG substitution) to 7% diesel (93% NG substitution) there were large uncertainties in the metereing of fuel quantity at low diesel flow rates.

Hope this helps,
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Old   December 13, 2017, 18:01
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Quote:
Originally Posted by SamWijey View Post
The uncertainties checked for in the paper was determined by the industrial partner of the paper. They decided based on their experiments, that these uncertainties were possible. The NG mass flow rate was accurately measured at the inflow and hence the uncertainty of that was small. Since the same injector was used to inject 100% diesel (0% NG substitution) to 7% diesel (93% NG substitution) there were large uncertainties in the metereing of fuel quantity at low diesel flow rates.

Hope this helps,
Thank you so much.
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Old   December 13, 2017, 18:44
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Quote:
Originally Posted by SamWijey View Post
The uncertainties checked for in the paper was determined by the industrial partner of the paper. They decided based on their experiments, that these uncertainties were possible. The NG mass flow rate was accurately measured at the inflow and hence the uncertainty of that was small. Since the same injector was used to inject 100% diesel (0% NG substitution) to 7% diesel (93% NG substitution) there were large uncertainties in the metereing of fuel quantity at low diesel flow rates.

Hope this helps,
I have also problem with injection pressure in CONVERGE. I have the experimental data (injection duration=6, diesel injected mass=3 mg/cycle, hole diameter=0.00023). It gives me injection pressure of around 80-100 bar. However, based on the experiment the injection pressure is 525 bar. Did have this issue?
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Old   December 14, 2017, 04:42
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Hey guys,

This is an interessting conversation. I'd like to join you since I am also working on dual fuel simulation and it is very tricky, especially with low load and early injection!

For the rail Pressure: did you calculate Cd of the spray with converge tool? In my case using this chance rail pressure peak automatically matched the maximum one i set (525bar in your case).

However I have a second article that underlines importance of fuel temperature in Dual fuel engine with high percentage energy substitution. I found it interesting.

SAE 2012-01-0826
Controlling the Injector Tip Temperature in a Diesel Dual Fuel Engine.
F. Konigsson, P. Stalhammar
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