14. starptautiskā konference 2012 - Latvijas Jūras akadēmija

Proceedings of 14th International conference „Maritime Transport and Infrastructure - 2012”where A – the area of cylinder,p g – the pressure of compressed air in the system,s 2 – piston displacement from TDC to the point at which compressed air supplysuspendedn 1 – the polytropic indexV 2 – the volume of cylinder when air supply is suspended,V 3 – the volume of cylinder when exhaust is commencedThe work consumed during the compression W 2 is calculated as follows:W 2 =p a ∙V 4 – p c ∙V c( 2 )n 1 – 1Wherep a – atmospheric pressure, V 4 – the volume of cylinder when exhaust is commenced,p c , V c – the air pressure and the volume of cylinder at TDCAssuming that the water resistance force to the rotation is proportional to the propeller'sangular velocityM prop = k ∙ 2and friction losses taken into account the efficiency at engine starting , the efficient work Wachieved by engine with z cylinders during one revolution of the crankshaft could be approximatelydetermined as follows:W = z( ∙W 1 – W 2 ) – 2∙ k ∙ 2 .According to the theorem of kinetic energy change, crankshaft angular speed of one revolutionin the engine at starting to be determined from the relationship:0,5 J red ∙ ω 2 = Wor, taking in account expression:0,5 J red ∙ ω 2 = z( ∙W 1 – W 2 ) – 2∙ k ∙ 2 .where J red - simplified moment of inertia of the crankshaft with the pistons, connecting rods,flywheels, shaft and propeller after N revolutions:0,5 J red ∙ ω 2 = N [ z( ∙W 1 – W 2 ) – 2∙ k ∙ 2 ] ,Whence we find:0,5 JN =red ∙ ω 2 ( 3 )z( ∙W 1 – W 2 ) – 2∙ k ∙ 2Assuming that the crankshaft moves steadily accelerated at engine starting, starting time tdetermined from the relationship:4 π ∙ Nt =( 4 )ωThe consumption of compressed air and necessary volume of starting air receiverThe consumption of compressed air for one cylinder during one revolution of the crankshaft isslightly less than V 2 . So during N revolutions total air consumption is:Q < N ∙ z∙V 2 .As the compressed air receivers must run at least n times, the total air consumption will be:65