One approach to avoid the soot/NOx-trade-off in conventional diesel engines is to reach a homogeneous air to fuel mixture before the start of combustion (SOC). There are already existing solutions for homogeneous mixtures with diesel fuel. Therefore, the diesel fuel must be vaporized before injection to reach comparable brake-specific fuel consumption (BSFC) to conventional diesel combustion without significant cylinder wall and piston impingement. However, with this type of homogeneous charge compression ignition (HCCI) it is impossible to control the combustion with the injection pattern and therefore it is not practical for robust ECU mapping. Hence, HCCI has never qualified for serial use.
One way to counteract the resulting variance in SOC is a partially premixed charge in the combustion chamber before SOC. A high rate of exhaust gas recirculation (EGR) with injection-controlled combustion leads to ultra-low soot and NOx emissions in a so-called premixed charge compression ignition (PCCI) application. The possibility to use state-of-the-art components such as serial injectors, pistons and EGR system of conventional diesel engines qualifies PCCI for serial use. Furthermore, the pressure gradients are comparable to those of standard diesel combustion, which leads to known combustion noise and mechanical stress of the engine.
In this project, a single-cylinder Mercedes-Benz engine is used to investigate PCCI combustion at IFS University of Stuttgart. The engine is fully equipped with pressure transducers (intake, in‑cylinder and exhaust). Boost and exhaust pressure are regulated externally. The high temperature EGR rate can be varied depending on the operating points. In addition, injection strategies and intake air temperature can be set independently in a wide range to gain a maximum spread of experimental data as basis for the simulation.
The goal of this project is to establish a 0D-/1D-approach to predict ignition delays (ID) for PCCI operation with multiple injection strategies. Low and high-temperature combustion can be observed in many operating points. Therefore, the physical and chemical ID of low and high temperature combustion have to be validated regarding different injection strategies, EGR rates, intake and exhaust pressures, intake temperatures and engine load.
An Empirical Based Model to Predict Ignition Delays in Partially Premixed Compression Ignition Mode
Proceedings
2022-03-14
14 pages
Article/Chapter (Book)
Electronic Resource
German
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