14. starptautiskā konference 2012 - Latvijas Jūras akadēmija

Proceedings of 14th International conference „Maritime Transport and Infrastructure - 2012”THE METHOD OF STARTING AIR SYSTEM CALCULATIONRihards Indriksons*, Janis Kokars**, Igors Kurjanovics****Latvian Maritime Academy, Flotes str. 5B, LV-1016, Latvia, E-mail: rihards1940@inbox.lv**Latvian Maritime Academy, Flotes str. 5B, LV-1016, Latvia, E-mail: janis.kokars@latja.lv***Riga Technical University, Kalku str. 1, LV-1016, Latvia, E-mail: igors.kurjanovics@rtu.lvAbstractThis article deals with a method of calculation for diesel engine compressed air starting systems. Themethod is based on a comparison of the effective work done by the compressed air and the workrequired to compress air during the compression stroke. Correlations have been found between theapproximate time to start the engine and the pressure in the starting air receiver as well as thecompressed air consumption. The approximate correlations for calculating the pressure drop inreceivers, depending on the receiver volume and the volume of air consumption at engine starting,were given. A six cylinder slow speed engine was used in these calculations as an example.KEY WORDS: starting system, efficient work, air receiver.IntroductionOver the past 20 years, the design of ship’s main engines has undergone radical changes.Notable changes of cylinder thermodynamic work cycle parameters are observed. An increase ofthese parameters is associated with the need to increase the relative power and the cylinder indicatedpower efficiency. Significantly increasing the engine stroke to diameter ratio from 1.7 to 2.2 - 2.5 hasincreased thermal and mechanical loads.In the calculation on the basis of LPG tanker's "Kurzeme" main engine MAN B & W 6S50MC parameters, it is evident that the ratio Pz/ Pc, or so-called pressure increase ratio (Lambda), withsignificant increase in the parameters has been reduced to 1,1 - 1,3 instead of the previous 1,4-1,5.This proves the tendency for the transition to greater R in the diesel cycle.The compression pressure in cylinder is equal to 98-100 bars and the maximum combustionpressure reaches 130 bars. Such changes in construction and parameters are making a significantimpact on the engine starting and reversing processes. These processes are significant for mainengines coupled directly to the ship's propeller, despite being of short duration. Although changes inparameters have been made the pressure in starting air vessel remains the same - maximum 30 bars.Calculations are required to ensure correct starting and reversing in the future as Pzandcontinue to grow.PcStarting duration and rotation speed of crankshaft at the end of startingThe work made by air during one revolution of crankshaft at starting of engineW 1 = W 1 * + W 1 ** ,WhereW 1 * – the work made by compressed air during the air supplyW 1 ** – the work made by compressed air after the air supply suspensionW 1 * = A ∙ p g ∙ s 2 ; W 1 ** =p g ∙ V 21 –n 1 – 1 V 3V 2n 1 - 1( 1 )64