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Diesel distributor fuel-injection pumps

Diesel-engine management

Technical Instruction

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©Robert Bosch GmbH, 1999 Postfach 300220, D-70442 Stuttgart. Automotive Equipment Business Sector, Department for Automotive Services, Technical Publications (KH/PDI2).

Editor-in-Chief: Dipl.-Ing. (FH) Horst Bauer.

Editors: Dipl.-Ing. Karl-Heinz Dietsche, Dipl.-Ing. (BA) Jürgen Crepin, Dipl.-Holzw. Folkhart Dinkler, Dipl.-Ing. (FH) Anton Beer.

Author: Dr.-Ing. Helmut Tschöke, assisted by the responsible technical departments of Robert Bosch GmbH.

Presentation: Dipl.-Ing. (FH) Ulrich Adler, Berthold Gauder, Leinfelden-Echterdingen.

Translation: Peter Girling.

Photographs: Audi AG, Ingolstadt and Volkswagen AG, Wolfsburg.

Technical graphics: Bauer & Partner, Stuttgart.

Unless otherwise specified, the above persons are employees of Robert Bosch GmbH, Stuttgart.

Reproduction, copying, or translation of this publication, wholly or in part, only with our previous written permission and with source credit. Illustrations, descriptions, schematic drawings, and other particulars only serve to explain and illustrate the text. They are not to be used as the basis for design, installation, or delivery conditions. We assume no responsibility for agreement of the contents with local laws and regulations. Robert Bosch GmbH is exempt from liability, and reserves the right to make changes at any time.

Printed in Germany. Imprimé en Allemagne.

4th Edition, April 1999. English translation of the German edition dated: November 1998.

Combustion in the diesel engine The diesel engine2

Diesel fuel-injection systems: An overview Fields of application4 Technical requirements 4 Injection-pump designs 6

Mechanically-controlled (governed) axial-piston distributor fuel-injection pumps VE Fuel-injection systems 8 Fuel-injection techniques 9 Fuel supply and delivery12 Mechanical engine-speed control (governing) 2 Injection timing29 Add-on modules and shutoff devices32 Testing and calibration45 Nozzles and nozzle holders46

Electronically-controlled axialpiston distributor fuel-injection pumps VE-EDC54

Solenoid-valve-controlled axial-piston distributor fuel-injection pumps VE-MV60

Start-assist systems 62

Diesel distributor fuel-injection pumps VE

The reasons behind the diesel-powered vehicle’s continuing success can be reduced to one common denominator: Diesels use considerably less fuel than their gasoline-powered counterparts. And in the meantime the diesel has practically caught up with the gasoline engine when it comes to starting and running refinement. Regarding exhaustgas emissions, the diesel engine is just as good as a gasoline engine with catalytic converter. In some cases, it is even better. The diesel engine’s emis- sions of CO2, which is responsible for the “green-house effect”, are also lower than for the gasoline engine, although this is a direct result of the diesel engine’s better fuel economy. It was also possible during the past few years to considerably lower the particulate emissions which are typical for the diesel engine. The popularity of the high-speed diesel engine in the passenger car though, would have been impossible without the diesel fuel-injection systems from Bosch. The very high level of precision inherent in the distributor pump means that it is possible to precisely meter extremely small injection quantities to the engine. And thanks to the special governor installed with the VE-pump in passenger-car applications, the engine responds immediately to even the finest change in accelerator-pedal setting. All points which contribute to the sophisticated handling qualities of a modernday automobile. The Electronic Diesel Control (EDC) also plays a decisive role in the overall improvement of the diesel-engined passenger car. The following pages will deal with the design and construction of the VE distributor pump, and how it adapts injected fuel quantity, start-of-injection, and duration of injection to the different engine operating conditions.

The diesel engine

Diesel combustion principle

The diesel engine is a compressionignition (CI) engine which draws in air and compresses it to a very high level. With its overall efficiency figure, the diesel engine rates as the most efficient combustion engine (CE). Large, slow-running models can have efficiency figures of as much as 50% or even more. The resulting low fuel consumption, coupled with the low level of pollutants in the exhaust gas, all serve to underline the diesel engine’s significance. The diesel engine can utilise either the 4- or 2-stroke principle. In automotive applications though, diesels are practically always of the 4-stroke type (Figs. 1 and 2).

Working cycle (4-stroke)

In the case of 4-stroke diesel engines, gas-exchange valves are used to control the gas exchange process by opening and closing the inlet and exhaust ports.

Induction stroke During the first stroke, the downward movement of the piston draws in unthrottled air through the open intake valve.

Compression stroke During the second stroke, the so-called compression stroke, the air trapped in the cylinder is compressed by the piston which is now moving upwards. Compression ratios are between 14:1 and 24:1. In the process, the air heats up to temperatures around 900°C. At the end of the compression stroke the nozzle injects fuel into the heated air at pressures of up to 2,0 bar.

Power stroke Following the ignition delay, at the beginning of the third stroke the finely atomized fuel ignites as a result of auto-ignition and burns almost completely. The cylinder charge heats up even further and the cylinder pressure increases again. The energy released by the ignition is applied to the piston. The piston is forced downwards and the combustion energy is transformed into mechanical energy.

Exhaust stroke In the fourth stroke, the piston moves up again and drives out the burnt gases through the open exhaust valve. A fresh charge of air is then drawn in again and the working cycle repeated.

Combustion chambers, turbocharging and supercharging

Both divided and undivided combustion chambers are used in diesel engines

Combustion in the diesel engine

Combustion in the diesel engine

Principle of the reciprocating piston engine

TDC Top Dead Center, BDC Bottom Dead Center.

VhStroke volume, VCCompression volume, sPiston stroke.

Fig. 1

UMM0001ETDC BDC

BDC Vh

(prechamber engines and direct-injection engines respectively).

Direct-injection (DI) engines are more efficient and more economical than their prechamber counterparts. For this reason, DI engines are used in all commercial-vehicles and trucks. On the other hand, due to their lower noise level, prechamber engines are fitted in passenger cars where comfort plays a more important role than it does in the commercial-vehicle sector. In addition, the prechamber diesel engine features considerably lower toxic emissions (HC and

NOX), and is less costly to produce than the DI engine. The fact though that the prechamber engine uses slightly more fuel than the DI engine (10...15%) is leading to the DI engine coming more and more to the forefront. Compared to the gasoline engine, both diesel versions are more economical especially in the part-load range.

Diesel engines are particularly suitable for use with exhaust-gas turbochargers or mechanical superchargers. Using an exhaust-gas turbocharger with the diesel engine increases not only the power yield, and with it the efficiency, but also reduces the combustion noise and the toxic content of the exhaust gas.

Diesel-engine exhaust emissions

A variety of different combustion deposits are formed when diesel fuel is burnt. These reaction products are dependent upon engine design, engine power output, and working load. The complete combustion of the fuel leads to major reductions in the formation of toxic substances. Complete combustion is supported by the careful matching of the air-fuel mixture, absolute precision in the injection process, and optimum air-fuel mixture turbulence.

In the first place, water (H2O) and carbon dioxide (CO2) are generated. And in relatively low concentrations, the following substances are also produced:

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