# 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
As the engine load increases, a greater quantity of fuel is injected per cycle, resulting in higher oxygen consumption during combustion and a significant reduction in the oxygen concentration in the exhaust gases; the excess air ratio also decreases due to the greater amount of air required for complete fuel combustion. In the case of EGR on, as the engine load increases (BMEP = 0.2 MPa, 0.4 MPa, and 0.6 MPa), the O\({}_{2}\) concentration in the exhaust gases relatively decreases by approximately 17%, 18%, and 22% respectively, compared to EGR off (Figure 8a). The calculated \(\lambda\) also decreases due to EGR on, by approximately 29%, 24%, and 22%, respectively (Figure 8b). At lower loads, \(\lambda\) decreases more sharply than the observed O\({}_{2}\) concentration in the exhaust gases, as under lean mixture conditions, the oxygen concentration is less sensitive to EGR-induced dilution. In the case of EGR off, increasing the HEE intensity up to 100% resulted in a more pronounced effect, and at higher loads, the O\({}_{2}\) concentration was relatively increased by up to 3.6%, while \(\lambda\) rose by up to 5%. In the case of EGR on, the O\({}_{2}\) concentration increased by up to 1.2%, and \(\lambda\) increased by up to 3%. This leads to improved combustion efficiency. However, in the case of EGR off, increasing HEE intensity leads to a rise in \(\lambda\) across the entire load range, while under EGR on conditions, HEE intensification increases \(\lambda\) at lower engine loads, but the positive effect of HEE diminishes as the load increases. As the engine load increases, the exhaust gas temperature (\(T_{ex}\)) rises due to the greater amount of energy released from the combustion of a larger mass of injected fuel. When the EGR valve is opened, \(T_{ex}\) increases (Figure 9a) as a result of the slower combustion process caused by the reduced oxygen concentration and the presence of CO\({}_{2}\) in the recirculated exhaust gases within the cylinder. As the HEE increases to 50% and 100%, the \(T_{ex}\) decreases by up to 22 \({}^{\circ}\)C and 20 \({}^{\circ}\)C, respectively, under both EGR off and EGR on conditions. A greater reduction in \(T_{ex}\) is observed at higher loads, as the additional air supply during combustion becomes more significant due to the increased fuel quantity. This reduction induces an increase in combustion rate and thermal efficiency, as less energy is lost through the exhaust system. Figure 7: Change in intake air mass flow. The temperature of the recirculated exhaust gases (\(T_{EGR}\)) correlates with \(T_{ex}\) but is 30 \({}^{\circ}\)C to 45 \({}^{\circ}\)C lower (Figure 9b) due to the low-intensity cooler integrated into the EGR system. Even a modest decrease in \(T_{EGR}\) can significantly lower the overall intake temperature and thereby improving cylinder filling. Enhanced air charging improves the combustion process, leading to reduced carbon monoxide (CO) and HC emissions, as well as lower smoke levels. Introducing a cooler mixture into the cylinder lowers the compression and combustion temperatures, resulting in reduced NOx emissions. Improved combustion also contributes to lower fuel consumption and, consequently, reduced CO2 emissions.