Dear Khaleel

I wish the following articles will be of great help to you.

- Chaichan M T, Combustion and Emissions Characteristics for DI Diesel Engine Run by Partially-Premixed (PPCI) Low Temperature Combustion (LTC) Mode, International Journal of Mechanical Engineering (IIJME), vol. 2, No. 10, pp: 7-16, 2014.

- Chaichan M T, Salam A Q & Abdul-Aziz S A, Impact of EGR on engine performance and emissions for CIE fueled with diesel-ethanol blends, Arabic universities Union Journal, vol. 27, No. 2, 2014.

-Chaichan M T, Abass Q A, Effect of cool and hot EGR on performance of multi-cylinder CIE fueled with blends of diesel and methanol, Al-Nahrain Collage of Engineering Journal, vol. 19, No. 1, pp: 76-85, 2016.

Dear Khaleel

There are no specific limit to EGR level to be added. It depends manily on the combustion mode. If we are talking about ordinary mode the acceptable level don't exceed 20%, but if we are talking about HCCI, PCCI, or LTC modes the EGR levels may exceed 40%.

Regards

Dear Khaleel

I wish the following articles will be of great help to you.

- Chaichan M T, Combustion and Emissions Characteristics for DI Diesel Engine Run by Partially-Premixed (PPCI) Low Temperature Combustion (LTC) Mode, International Journal of Mechanical Engineering (IIJME), vol. 2, No. 10, pp: 7-16, 2014.

- Chaichan M T, Salam A Q & Abdul-Aziz S A, Impact of EGR on engine performance and emissions for CIE fueled with diesel-ethanol blends, Arabic universities Union Journal, vol. 27, No. 2, 2014.

-Chaichan M T, Abass Q A, Effect of cool and hot EGR on performance of multi-cylinder CIE fueled with blends of diesel and methanol, Al-Nahrain Collage of Engineering Journal, vol. 19, No. 1, pp: 76-85, 2016.

EGR is employed to reduce engine-out NOx emissions by simultaneously reducing combustion temperature and O2 concentration in the engine cylinder. However, there are complex trade-offs between the benefit that EGR brings and the issues it creates:

1.  EGR reduces engine efficiency due to thermodynamic reasons.

2.  It increases PM formation.

3.  Recirculated exhaust gas needs to be cooled to achieve NOx reduction goals, which increases system complexity. EGR cooler and valve are subject to fouling.

4.  It compromises engine durability.

The maximum EGR ratio is determined by the balance of all the above factors. Some engines could run at very high EGR ratio (60% or slightly higher), but the actual ratio would be lower when other alternatives are available to help achieve NOx reduction goals. EGR ratio typically varies in the 0-40% range. Definitely not every-oem likes EGR.

There really is not sufficient information in your question about the type of engine you are using or its combustion and mixing processes to adequately answer.  There are a number of operational limits placed on EGR but they differ for spark ignition vs. diesel engines, cooled vs. uncooled EGR, and may differ depending on EGR flow distribution differences between cylinders in multi-cylinder engines.  Dilute HCCI combustion using a low-reactivity fuel may use 50-60% EGR.  A GDI spark-ignited engine with turbocharging might use 15% cooled-EGR at some operational points and begin to encounter unacceptable COV of IMEP and/or misfire.  Inducing intake port tumble into the engine design might allow 20-25% cooled-EGR at the same operational points. A diesel may encounter unacceptable fuel pyrolysis and soot formation at EGR rates of 30% at some operational points or might perfectly fine depending on a number of factors that impact burn rate and combustion phasing (injection pressure, timing of multiple injections, combustion system design, EGR temperature, etc.).

I suggest that you conduct a thorough literature search on this topic and limit your search to the particular engine type and combustion type that you are interested in.