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Power unit – engine
Published in Andrew Livesey, Motorcycle Engineering, 2021
The cylinder head is fitted with inlet valves; these open and close to control the flow of the petrol and air mixture from the inlet manifold into the combustion chamber. The cylinder head is also fitted with exhaust valves to control the flow of the spent exhaust from the combustion chamber into the exhaust manifold and exhaust system. The passage in the cylinder head, which connects the manifold to the combustion chamber, is called the port. There are inlet ports and exhaust ports. The valves are situated where the ports connect into the combustion chamber. The valves are operated by the camshaft; this is discussed later in this chapter.
Reciprocating Engines
Published in Neil Petchers, Combined Heating, Cooling & Power Handbook: Technologies & Applications, 2020
The cylinder head (or heads) forms the top or lid to seal the cylinders. Cylinder heads are typically made of cast iron or aluminum and must be strong and rigid to distribute the gas forces acting on the head as uniformly as possible through the engine block. The cylinder head contains the spark plug or fuel injector and, in over-head valve engines, parts of the valve mechanisms.
Engine systems
Published in Tom Denton, Automobile Mechanical and Electrical Systems, 2018
Cylinder heads are cast from aluminium alloy or iron. Aluminium alloy is lighter but cast iron or steel valve seats and guides must be installed in the head (Fig. 2.84). Cast iron heads generally have valve seats and guides formed directly in the head material.
Refractory/steel/inclusion interactions in Al-deoxidised valve spring steel treated with Na2CO3
Published in Canadian Metallurgical Quarterly, 2019
Liangjun Chen, Weiqing Chen, Wei Yan, Yindong Yang, Alexander McLean
Valve spring is a helical spring used to hold closed a valve in the cylinder head of an internal-combustion engine. During working, it is subjected to periodical loads at a very high frequency. This makes valve spring very sensitive to inclusions and inclusions with poor deformability may initiate cracks, followed by fatigue fracture [1,2]. There are two main strategies for inclusion control in valve spring steel nowadays. One is to generate softer, less harmful, low melting point inclusions by employing Si–Mn deoxidation combined with low basicity slag refining. However, this does not always work well because of the poor level of cleanliness caused by the weak affinity of Si and Mn for oxygen [3]. The other strategy is to improve the cleanness by utilising the strong deoxidising power of Al [4,5]. However, the generated Al2O3 inclusions (M.P. 2327 K) or MgO·Al2O3 inclusions (M.P. 2408 K) may become crack initiations due to their high hardness. In addition, the submerged entry nozzle may be blocked by agglomerative inclusions with a high melting point [6].
Cylinder Head Bolt Tightening Strategies in Case of Multi-Cylinder Engines and Its Effect on Gasket Sealing Performance, Bore Deformation and Piston Ring Conformability
Published in Australian Journal of Mechanical Engineering, 2020
Abhijeet V. Marathe, G. Venkatachalam, Neelkanth V. Marathe
The cylinder head gasket is the most critical sealing element in the internal combustion engine. The area of the gasket, around the cylinder, must be robust enough to withstand the pressures that are exerted on the pistons while ensuring that there is no leakage of coolants or combustion gases. It must be able to accomplish this at all engine temperatures and pressures without malfunction, as the failure of the engine gasket usually results in a breakdown of the entire engine. Having adequate pressure distribution in the gasket at these critical sealing areas is of utmost importance. It also affects engine piston ring conformability in the cylinder bore, engine blow-by and lubricant oil consumption. During assembly of the cylinder head gasket joint, there is a loss of bolt preload and consequently, a reduction of compression force on the gasket when the bolts are tightened sequentially. This leads to the reduction of contact pressure in the gasket, which causes leakages. To obtain the required gasket sealing pressure at the critical sealing areas, it is necessary to combat this problem of bolt preload reduction. It is observed that the ‘bolt preloads applied for tightening the bolts’ and ‘the numbers of passes in which these preloads are applied’ are critical parameters affecting the bolt preload loss during tightening. Also, the sequence or pattern of tightening the bolts joining the mating surfaces plays a significant role in deciding the final bolt preload retention after complete tightening. In this regard, considerable number of investigations is reported in the literature in case of gasket pipe flange joints mostly found in pressure vessel applications. As per the same analogy, the methods of reducing bolt preload scatter in case of engine cylinder head gasket joints can be investigated. Cylinder head gasket joint is a slab in nature while Pipe flange joint of the pressure vessel is circular. The analogy is not directly applicable to the cylinder head gasket joint but can be explored. Experimental procedures are quite expensive and laborious for analysing the effect of various tightening strategies. Hence there is a need to find a numerical and analytical process through which the impact of such approaches can be examined. A primary tool used in this regard is Finite Element Analysis (FEA). But one must overcome the lack of an accurate and well-correlated methodology for modelling cylinder head gasket joint, which can capture the effects of the bolt tightening sequences while providing the gasket performance parameters like contact pressure distribution and gasket closure.