A Study on the Improvement of Marine Diesel Engine Transient Performance by Means of Air Injection

This dissertation, "A Study on the Improvement of Marine Diesel Engine Transient Performance by Means of Air Injection" by Fang, Wei, 魏昉, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled A STUDY ON THE IMPROVEMENT OF MARINE DIESEL ENGINE TRANSIENT PERFORMANCE BY MEANS OF AIR INJECTION Submitted by Wei Fang for the degree of Doctor of Philosophy at The University of Hong Kong in October 2005 When ship is sailing at sea, it finds it difficult to stop if sudden danger emerges ahead due to its considerable inertia. The most feasible method of stopping is to pull back the vehicle compulsorily by its prime mover. Direct connected turbocharged diesel engines are used by most large volume, slow speed oceangoing merchant ships. The slow response of the turbocharged system under sudden acceleration is the major problem in accelerating the engine after it is put in reverse. In this study the method of additional air injection is adopted to augment the inlet air mass flow rate at the moment of engine acceleration, so as to optimize the combustion inside the cylinder and output greater torque, therefore mitigating the retardation of the turbocharger. Additional air is injected at the exit of the compressor. Different injection timings and durations are compared under different working conditions. The transient values of fourteen major engine parameters are acquired to analyze engine performance, including engine torque, speed, turbocharger speed, inlet and exhaust pressures and temperatures and load and fuel settings. In order to simulate the real marine engine, the exhaust system of the test- bed engine is modified from pulse turbo-charging to constant pressure turbo- charging, to study the effect of additional air on engine performance. In the experiments, the windmilling effect of the propeller has to be considered during the initiation of the transient manoeuvre concerning the behavior of load. Results show that additional air injection makes it considerably easier for a heavy loaded engine to accelerate, by helping to improve turbocharger response. The preferable injection duration depends on the amount of air required by the engine during the maneuver. The moment of additional fuel injection is the most appropriate timing of additional air injection. The effect of the additional air injection is less for a pulse turbocharged engine than a constant pressure turbocharged engine, which is widely used as marine ship prime mover. The study demonstrates that the technique of additional air injection can help to stop a marine vehicle faster when it encounters sudden danger. DOI: 10.5353/th_b3683484 Subjects: Diesel motor - Turbochargers Marine diesel motors