**8. Summary**

Diesel emissions and mitigations are complex and can be discussed in diverse topics as highlighted in this piece. Understanding of the subject matter involves good grasp of the engine systems designs, and interplay of relevant integrated technologies. The operational perspectives also demand attention. This starts with the nature of diesel fuel itself, how it is delivered to the engine, mixed and burnt with oxygen of the air. The efficiency of the in-cylinder combustion is central to the quality of emission occurring at the tail pipe. Inevitably, combustion event varies from cycle to cycle according to engine load requirements. Therefore even the best designed engines are prone to emit some unwanted pollutants into the atmosphere. To combat this, aftertreatment devices are now complementary to the overall engine technology.

The key after-treatment technologies have been briefly presented as independently considered techniques with respect to the variables they address. However this was for narrative convenience, as their inclusion extends the integration requirements of the engine. In a modern diesel engine especially for automotive applications, it is now customary that the exhaust train carry oxidation catalysts where CO, SOF and HCs are essentially oxidized to CO2 and water. Further, NO is oxidized to NO2 which in turn becomes an oxygen carrier for catalytic soot regeneration in the DPF and reduces back to NO. Then NO is reduced to elemental nitrogen through a SCR (**Figure 15**).
