Investigation of diesel injector nozzle tip temperature

Common Rail Diesel Injection (CRI) is the name of the fuel injection system which is used in modern diesel engines. This system transfers diesel fuel from fuel tank to common rail and provides the required fuel with the increased injection pressure like 2000-2500bar into combustion chamber. The main target of this system is to inject diesel fuel with the correct quantity, injection pressure and timing. In view of today, fuel consumption needs and emission regulations show that injection system has the most important role in engine. And the most critical part of diesel injector is nozzle body which is faced with very high temperatures during combustion. Injected fuel comes from the spray holes on injector nozzle body which is located in combustion chamber. Injector nozzle body is exposed to very high temperatures in each cylinder of the engine. So dynamic engine conditions affect the nozzle body design and material selection. With the assessment of engine working conditions, nozzle body material is selected, required heat treatment process and coating type/process are defined for this specific engine application. Maximum temperature is the most important input for the definition of these design details. Nozzle is pre-designed based on the given informations about customer engine application and sent to customer for engine/vehicle test. According to the temperature values and hardness decrease of the tested nozzle, it is confirmed or re-designed for final release. Under dynamic engine conditions, material characteristic, correlation between temperature and hardness decrease must be correctly formulated, the effects of these parameters must be totally understood. In the last years, emission regulations (Euro 5, Euro 6…) are getting harder and the temperatures which affect the material hardness are changing day by day. So having more knowledge or understanding about the critical parameters and effects of them is necessary. In this study, different engine test cycles which can cause very high temperatures in combustion chamber were performed and nozzle body hardness decreases were investigated. According to the investigation of the nozzles which were tested with different test cycles and durations, the definition of the most critical engine condition was aimed. The main focus was to understand the effects of the engine parameters on hardness decrease. The optimum condition was defined for the right material selection and reliable nozzle designs.