LN05 - Internal Combustion Engines ME422 Yeditepe...

Info iconThis preview shows pages 1–8. Sign up to view the full content.

View Full Document Right Arrow Icon
1 Internal Combustion Engines – ME422 Yeditepe Üniversitesi Gas Exchange Process Prof.Dr. Cem Soru ş bay Internal Combustion Engines Gas Exchange Process ¾ Introduction ¾ Valve mechanisms ¾ Induction in engines ¾ Scavenging in 2-stroke engines ¾ Parameters effecting induction and scavenging ¾ Volumetric efficiency
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2 Introduction This section deals with fundamentals of gas exchange process - intake and exhaust in 4-stroke engines, and scavenging in 2-stroke engines. The purpouse is to remove the burnt gases at the end of the power stroke and admit fresh charge for the next cycle. The power output of an engine at a given speed is proportional to the mass flow rate of air. Inducting the maximum air mass at wide-open throttle or full load is the primary goal for gas exchange process. Gas exchange process is characterizzed by overall parameters like volumetric efficiency (4-stroke) and scavenging and trapping efficiency (2-stroke) - these depend on design of engine subsystems like manifolds, valves, ports, as well as engine operating conditions. Supercharging and turbocharging are used to increase air flow through engines and hence power density. Introduction
Background image of page 2
3 Introduction Introduction
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
4 Introduction Valve Mechanism Rocker arm Inlet valve Exhaust valve Push rod Cam follower Camshaft
Background image of page 4
5 Valve Mechanism Valve Mechanism
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
6 Valve-operating Systems In engines with overhead poppet valves , the camshaft is either mounted in the cylinder block or in the cylinder head ( overhead camshaft -OHC) . In OHC engines, camshaft can be mounted directly over the valve stems, or it can be offset - offset valves are operated by rockers and valve clearences can be adjusted by altering pivot height. The drive is by chain or toothed belt. Valve seat inserts are used, especially for engines with alluminium alloy cylinder head to ensure minimum wear - poppet valves rotate to even out any wear and to maintain good seating. Engines with inlet and exhaust valves not placed in line, can use various push rod mechanisms or double overhead camshafts (DOHC) - one for inlet valves and other for exhaust valves. Valve-operating Systems
Background image of page 6
7 Valve Timing 4-stroke engines valve timing and p ~ V diagram for gas exchange process p V o 4 o 5 o 6 o 1 o 1 o 5 o 6 o 4 ÜÖN AÖN (EgA) (EgK) (EgA) (EmA) (EmA) (EmK) (EmK) (EgK) p r p a p e e r p e p r ÜÖN AÖN α =0-40 α =0-40 α =5-90 α =20-90 Krank dairesi 5 1 Emme süpab› aç›k 4 6 Egzoz süpab› aç›k Induction IVO inlet valve opening 0 - 40 (10 - 25) o CA BTDC when intake valve is closed, the p behind the valve is the sum of static and dynamic pressures. When the valve is opened, the pressure p r is greater than cylinder pressure and gases flow into the cylinder. This early opening depends on the gas velocities and the geometry of the intake manifold (cross section area etc) To be able to use the pressure wave action, IV can be opened up to 5 - 10 o CA ATDC in some engines.
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 8
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 10/04/2011 for the course ME 422 taught by Professor Cemsoruşbay during the Spring '11 term at Yeditepe Üniversitesi.

Page1 / 26

LN05 - Internal Combustion Engines ME422 Yeditepe...

This preview shows document pages 1 - 8. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online