Question

With reference to electronically controlled engines:

(a) Describe how fuel injection quantity and timing is adjusted. (6).

(b) Describe how the exhaust valve timing may be varied. (5)

(c) Describe how starting air valves are regulated. (5)

Answer 1

Part (a)

To be able to time the fuel injection the control system must know the crank angle of the individual units. To do this two crank angle sensors are fitted at the free end of the engine. These sensors are accurate to 0.1°. Each cylinder has its own electronic control system comprising of a cylinder control module and a variable driver module. Each Cylinder Control Module calculates the correct injection start angle, taking into account dead time, VIT, and Fuel Quality Setting. It also controls the quantity of fuel injected and the sequence of injection (i.e. for low load running).

When the Rail Valves are energised for injection by the Valve Driver Module, oil from the Control Oil Rail opens the Injection Control Valves. The fuel injectors are pressurised and fuel oil pressure behind a Fuel Quantity Piston in the Volumetric Control Unit maintains this pressure at the injectors. As the Piston moves to the left a feedback signal is sent to the Cylinder Control Module

When the desired amount of fuel has been injected the Valve Driver Module energies the solenoids which move the Rail valves back to the return position. The Injection Control Valves interrupt the supply to the injectors, and the increase in pressure on the LH of the fuel Quantity Piston moves it back to its starting position.

Part (b)

Part (c)

Starting Air System

The starting air system of the RT-flex engine is similar to that of a standard RTA engine except for the control of the cylinder starting air valves which is incorporated in the WECS rather than a starting air distributor. Starting air is supplied to the engine starting air manifold from the starting air receivers via the starting air shut-off valve. Individual cylinders are supplied with starting air via branch pipes which have flame arresters (Figure below).

The cylinder starting valve is operated by pilot air and the pilot air valve is controlled electrically by the cylinder control module. The starting pilot air valve is opened and closed directly by the cylinder control module (CCM) once every revolution at defined crank angles during the starting period.

When the engine has started the starting system is shut down. The opening and closing of the starting pilot valves is controlled by the corresponding CYL-EU, depending on the crank angle. The nominal opening angle is Zero degree (0°) and the closing angle is 110 degree (110°).

The automatic main starting valve is controlled by the COM-EU. Each MCM has its own start control valve. For slow turning the automatic valve is controlled and the starting pilot valves are pulsed via the CYL-EUs to reach the desired slow turning speed

✓ Verified Model Answer (Text Solution)

Starting Air System