# Impact of Heat Exchanger Effectiveness and EGR on Energy and Emission Performance of a CI Engine
## 3 Results and Discussion  
### Parameters of the Air-Exhaust Gas Mixture Supplied to the Engine Cylinder  
With increasing engine load, the ECU increases the amount of fuel injected, which leads to a rise in exhaust gas flow and, consequently, an increase in the turbocharger boost pressure \(p_{boost}\) (Figure 4). However, when EGR is on, \(p_{boost}\) decreases by 6-8% compared to the EGR-off condition due to a substantial reduction in the mass of fresh air entering the cylinder. Increasing the HEE had no significant effect on \(p_{boost}\) under either EGR-on or EGR-off conditions. Since the turbocharger boost pressure is regulated by an open-loop ECU control strategy, \(p_{boost}\) is primarily determined by the energy content of the exhaust gases. While a higher HEE slightly increases the intake air mass, potentially raising exhaust energy, on the other hand, the improved combustion efficiency and faster burn rate resulting from the additional air tend to reduce it. Consequently, variations in HEE have no significant effect on exhaust energy and, therefore, on turbocharger boost pressure. The intake air temperature drop across the heat exchanger (\(\Delta T_{oxol}\)) was significantly influenced by the intensity of HEE, engine load, and EGR activat  
Figure 4: Boost pressure in the intake manifold. of BMEP = 0.4 MPa, \(\Delta T_{coal}\) reached 21 \({}^{\circ}\)C and 19 \({}^{\circ}\)C under EGR-off and EGR-on conditions, respectively, with HEE at 50%. At a higher load of BMEP = 0.6 MPa, \(\Delta T_{coal}\) reached 29 \({}^{\circ}\)C and 26 \({}^{\circ}\)C (Figure 5). When HEE was increased to 100% at BMEP = 0.6 MPa, \(\Delta T_{coal}\) reached 52 \({}^{\circ}\)C and 48 \({}^{\circ}\)C under EGR-off and EGR-on conditions, respectively. The intake manifold temperature (\(T_{in}\)), representing the temperature of the intake air and recirculated exhaust gas mixture, is approximately 40 \({}^{\circ}\)C to 50 \({}^{\circ}\)C higher under EGR-on conditions compared to EGR-off conditions (Figure 6). The temperature difference of the mixture entering the cylinder between EGR-on and EGR-off is greater at lower engine loads, as the EGR ratio is higher under low-load conditions. With a 100% increase in heat exchanger effectiveness, under EGR-off conditions and at engine loads of BMEP = 0.2 MPa, 0.4 MPa, and 0.6 MPa, \(T_{in}\) decreases by approximately 9 \({}^{\circ}\)C, 13 \({}^{\circ}\)C, and 11 \({}^{\circ}\)C, respectively. Under EGR-on conditions, \(T_{in}\) decreases by approximately 12 \({}^{\circ}\)C, 13 \({}^{\circ}\)C, and 12 \({}^{\circ}\)C, respectively. This temperature reduction increases the air density and improves the engine's volumetric efficiency. As the engine load increases, the intake air mass (\(B_{air}\)) rises (Figure 7) due to the increasing boost pressure (Figure 4). When the EGR system is activated (with EGR ratios of approximately 0.28, 0.22, and 0.19), \(B_{air}\) decreases by about 27%, 20%, and 18%, respectively, as part of the intake charge is replaced by recirculated exhaust gases. This substitution also raises the intake mixture temperature and reduces its density. With increasing HEE intensity, \(B_{air}\) shows an upward trend of up to 4.0% under EGR-off conditions, primarily due to reduced intake air temperature, which increases air density. Under EGR-on conditions,  
Figure 5: Temperature variations across the heat exchanger. Figure 6: Temperature variations in the intake manifold. the rise in \(B_{air}\) is limited to approximately 1.5%, as the intake air is more strongly heated, reducing its density. The engine ECU operates with an open-loop EGR control strategy but uses mass airflow sensor data to estimate the EGR rate: an increase in measured intake airflow indicates reduced EGR flow and a corresponding reduction in EGR valve opening, which the control algorithm attempts to return to within predefined target limits. In this study, it is relevant to analyze the measured oxygen concentration in the exhaust gases and the calculated excess air ratio (\(\lambda\)).