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Old 08-29-2013, 03:26 AM
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Ferrer Ferrer is offline
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1.2-litre VTi-FE petrol engine of high efficiency

The 3-cylinder engine has undergone several modifications: optimisation of the engine operational cycle, reduction of friction losses, hermomanagement... All of these advances lead to fuel economy improvements by 10% yet with power maintained at 68bhp (50kW).

The Miller Cycle is accentuated and the compression ratio modified from 11:1 to 16:1 to increase the engine's thermodynamic efficiency. This can lead to self-ignition of the mixture (or knock), which is potentially destructive. To prevent this, several actions were taken.

So, the rate of unburned elements in the combustion chamber is reduced by valves of increased diameter, redesigned exhaust pipes, a redesigned manifold, and an adapted valve lift pattern. Furthermore, the heat exchanges are optimised in the cylinder block due to coolant passages arranged between the cylinders. The coolant now passes through the cylinder head along its entire length to recover the heat around each source: combustion chambers, between injectors and spark plugs.

The engine adopts direct injection which, by means of very precise phasing with the closing of the cylinder, maximises the benefit of each molecule of fuel. The variable setting at the inlet and at the exhaust extends the range of optimum efficiency to the entire engine speed range, both at full load and partial load.

However, not all of these various developments favour power at high engine speed. So, the capacity is modified to 1,233cm3 by increasing the bore and the stroke (75mm x 93mm) to maintain the declared 68bhp (50kW). On the other hand, this progress benefits the maximum torque produced which increases by 25%.

All of the moving components are specific to the 208 HYbrid FE. The nitrated steel crankshaft, the titanium con rods and the aluminium-copper alloy pistons are cut from solid. So, their weight is reduced in spite of the increase in capacity; the con rods and Gudgeon pins being halved.

The friction losses are a challenge as they represent approximately 1/5th of the power consumed by an engine. On the 208 HYbrid FE, they are reduced by approximately 40% notably by the crankshaft, the pistons and the Gudgeon pin, the piston rings and the camshaft followers. These components are given a diamond-like Carbon coating and are geometrically optimised.

The weight of the cylinder head, also cut from a solid block, is halved due to the reduced thicknesses permitted by its design and the characteristics of the aluminium used. The coolant circuit and the inlet line are made by rapid prototyping of resins charged with glass fibres or carbon. To do this, the laser beam of a 3D printer fuses successive layers of aluminium powder. This produces a functional component quickly and more cheaply in the context of individual specialised manufacture.

Produced using the same process, the piston base jets serve here both to cool them on use under load and to heat the oil as quickly as possible on starting.

This virtuous circle affects all of the areas explored by this technological demonstrator. So, the size of the radiator is reduced, benefiting the aerodynamic properties. The alternator, the starter and the reverse gear are eliminated, reducing the weight, mechanical losses, but also in its overall dimensions.
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