چرخه موتور دیزل مبتنی بر PC و برنامه شبیه سازی سیستم های خنک کننده

This paper describes a PC-based Diesel Engine Cycle and cooling system SIMulation (DECSIM) program that was developed at the Australian Maritime College. DECSIM has been validated against a variety of marine engines and can be used to predict the steady state performance characteristics of two- and four-stroke diesel engines. The program may be used to obtain pressure-crank angle, pressure-volume, and heat release diagrams. Applications of DECSIM are discussed that show how the program can be used to assist marine engineers in fault diagnosis and designers to predict the thermal behaviour of combustion chamber components. The program may also be used to model cooling system behaviour, and so can be used by design engineers to optimize the dimensions of components such as heat exchangers and pumps with acceptable system pressure drop characteristics.

Diesel engine &nulation in use at the Australian Maritime College may be classified into two main areas: real-time simulation and engine cycle simulation. The diesel engine training simulator described by Pal [l] ia an example of how a real-time simulator ia wed at the College to impart operational and diagnostic fault finding skills to aspiring marine engineers. This simulator replicates the main machinery plant, of a 120,000 tonne Bulk Carrier including the main propulsion plant,, which is a seven cylinder Mitsubishi two-stroke, slow speed engine. It consieta of a simulated ship’s engine room, control room, separate instructor’s room, and minicomputer. Students are trained for normal engine room operations, such as preparing the plant for departure and arrival in port, aa well as emergency situations such a~ a total loss of electrical power and crash astern manoeuvreg. An important requirement for such a simulator is that it should faithfully model the machinery’s response behaviour in real time. Engine cycle simulation programs, on the other hand, may take several hours of computing time to model au engine’s transient response behaviour that may last only several seconds in real time. These programs can be used to predict thk performance of a variety of engines, including exhaust emissions, over a wide range of operating variables. Engine cycle simulation programs are widely used by engine manufacturers to provide information for the detail design of current and future engines.

In this paper, DECSIM, a PC-based computer simulation package for diesel engine performance predictions, has been described. The program has been designed using a modular concept and is thus easy to expand. The predictions of DECSIM have been compared with two medium speed four-stroke and two slow speed two-stroke marine diesel engines. The predicted performance of these engines under steady state operating conditions was in good agreement with the experimentally measured values. The greatest deviation was for the two-stroke diesel engines. This may be due to the single zone scavenging model used in DECSIM for two-stroke engines, which tends to underestimate the charging efficiency [19]. A more comprehensive scavenging model for two-stroke engines is being investigated as part of the ongoing development of DECSIM. However,the results obtained confirm the use of DECSIM for trend analysis predictions. It has been shown that DECSIM A.can be used aa a tool to assist marine engineers in fault diagnosis, can also be used for the prediction of average temperatures for combustion chamber components,can be used in conjunction with a finite element analysis study to predict temperature distribution within combustion chamber components, and can be used to model cooling system behaviour and establish system operating characteristics.