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contd...
| Table 6.2 |
Comparison of Performance and Emissions of Pilot Injection and Conventional Injection with Retarded Timing |
| |
Conventional Retarded Injection Timing |
Pilot Injection |
| NOx, g/ kW-h |
5.5 |
5.5 |
| PM, g/kW-h |
0.58 |
0.45 |
| HC, g/kW-h |
2.57 |
1.25 |
| BSFC, g/kW-h |
249 |
238 |
ELECTRONIC FUEL INJECTION (EFI) SYSTEMS
Electronically controlled fuel injection systems have the capability to fulfill the ideal injection rate requirements,. The EFI also are capable of providing multiple injections. Electronically controlled diesel fuel injection systems have the following advantages over the mechanically controlled injection systems as they provide:
- Very high injection pressures exceeding 2000 bar
- Precise control of injection timing.
- Precise fuel metering to control power output and limit smoke.
- Extremely low cylinder to cylinder variation in the quantity of fuel injected.
- Injection rate shaping with controlled initial rate of injection to reduce noise and emissions
- Sharp end-of-injection to eliminate nozzle dribble, prevent nozzle fouling and, reduce smoke and hydrocarbon emissions.
- Injection rate shaping for controlling heat release rates during pre-mixed and diffusion combustion phases for controlling smoke and NOx formation.
Electronically controlled unit injectors, distributor pumps and common rail injection systems are in use.
Electronic Unit Injectors
In the electronic unit injectors (EUI) the injection pumping element that raises the fuel to injection pressure and the injector nozzle are integrated into one unit. One each of the EUI is directly mounted on every engine cylinder. The injection pump plunger of every EUI is driven directly by the engine camshaft via a rocker arm. The electronic unit injectors were introduced on heavy-duty diesel truck engines in the USA around 1990 as these could develop much higher pressures than the in-line mechanical injection systems. A EUI design is shown in Fig. 6.5. In this design, metering of the fuel delivery is done by the plunger and the injection timing is controlled by opening and closing events of the solenoid valve of the EUI. Normally, the fuel from the plunger bypasses the solenoid valve and the fuel goes back to the return fuel line. As soon as the solenoid valve closes the fuel bypass passage, a high pressure is generated in the fuel passage above the
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