# Impact of Heat Exchanger Effectiveness and EGR on Energy and Emission Performance of a CI Engine
## 4 Conclusions  
The following key findings were obtained from the investigation of varying heat exchanger effectiveness (HEE) and EGR operation in a CI engine under part-load conditions:  
Figure 19: Effect of engine load and heat exchanger effectiveness on CO\({}_{2}\) variation.  
Figure 18: Effect of engine load and heat exchanger effectiveness on HC variation.  
1. EGR and air mass effects:  
- at BMEP levels of 0.2, 0.4, and 0.6 MPa, the ECU-controlled EGR rates were approximately 0.28, 0.22, and 0.19, respectively;  
- corresponding intake air mass reductions reached approximately 27%, 20%, and 18%;  
- with 100% HEE, intake manifold air temperature dropped by ~13 \({}^{\circ}\)C, while intercooler outlet temperature decreased by ~52 \({}^{\circ}\)C (EGR on) and ~48 \({}^{\circ}\)C (EGR off).  
2. Air mass and ECU regulation:  
- the ECU maintains the EGR ratio by adjusting boost pressure and monitoring intake air mass.  
- under EGR on, intake air mass increased only by ~1.5% at full HEE, whereas under EGR off, it rose by up to ~4%.  
3. Combustion and pressure dynamics:  
- under EGR off, enhanced air cooling raised compression pressure and ignition delay, boosting heat release rate and reducing exhaust gas temperature by up to 20 \({}^{\circ}\)C;  
- EGR on conditions, with higher CO\({}_{2}\) concentration, suppressed combustion intensity, lowering peak temperature by ~16%.  
4. Fuel consumption and efficiency:  
- EGR increased BSFC by 2-2.8% and exhaust gas temperature by 15-17% due to reduced combustion efficiency;  
- higher HEE partially mitigated these effects, improving combustion quality and reducing BSFC by up to 2.5%.  
5. Emissions:  
- under EGR-off, 100% HEE reduced:  
\(\odot\) smoke opacity by 15-18% due to increased air-fuel ratio (\(\lambda\));  
\(\odot\) specific NO\({}_{\rm x}\) emissions by 14-41% due to lower combustion temperatures;  
- under EGR-on, smoke opacity increased 4.3-6 times, with HEE reducing smoke by up to 14% only under low loads;  
- NO\({}_{\rm x}\) emissions decreased by 30-45% due to EGR alone, and up to 60% when combined with 100% HEE;  
- HC emission reduction with HEE was limited due to the offsetting effect of lower combustion temperature.  
- CO\({}_{2}\) emissions:  
\(\odot\) decreased by up to 3.0% under EGR off with higher HEE;  
\(\odot\) increased by up to 4% under EGR on, partially offset by HEE at lower loads.  
6. General implications:  
- under EGR off, high HEE intensity can partially substitute EGR by reducing NO\({}_{\rm x}\) and enhancing combustion;  
- under EGR on, HEE effectiveness is limited by ECU-imposed intake air constraints.  
- combined control of EGR and HEE is essential for balancing NO\({}_{\rm x}\) emissions and engine efficiency across operating ranges.  
Future work will focus on broader engine operation ranges and the use of renewable fuels (e.g., HVO, RME, synthetic fuels), supporting sustainable and efficient energy use.  
Conceptualization, A.R., and A.M.; methodology, A.R., and A.M.; software, A.R., and A.M.; validation, S.P., and A.R.; formal analysis, S.P.; investigation, A.M.; resources, A.R.; data curation, A.R.; writing--original draft preparation, A.R., S.P., and A.M.; writing--review and editing, S.P.; visualization, A.M.; supervision, A.R.; project administration, S.P. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The original contributions presented in the study are included in the article; further inquiries can be directed to the corresponding author.  
**Acknowledgments:** The authors prepared part of the paper using AVL BOOST engine modeling software, which was provided under the cooperation agreement between AVL Advanced Simulation Technologies and Vilnius Gediminas Technical University, Faculty of Transport Engineering.  
**Conflicts of Interest:** The authors declare no conflicts of interest.