Diesel-engine management Diesel distributor fuel-injection pumps Technical Instruction Published by: © Robert Bosch GmbH, 1999 Postfach 30 02 20, 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. Diesel distributor fuel-injection pumps VE The reasons behind the diesel-powered Combustion in the diesel engine vehicle’s continuing success can be The diesel engine 2 reduced to one common denominator: Diesels use considerably less fuel than their gasoline-powered counterparts. Diesel fuel-injection systems: And in the meantime the diesel has An overview practically caught up with the gasoline Fields of application 4 engine when it comes to starting and Technical requirements 4 running refinement. Regarding exhaust- Injection-pump designs 6 gas emissions, the diesel engine is just as good as a gasoline engine with Mechanically-controlled (governed) catalytic converter. In some cases, it is axial-piston distributor fuel-injection even better. The diesel engine’s emis- pumps VE sions of CO2, which is responsible for the “green-house effect”, are also lower Fuel-injection systems 8 than for the gasoline engine, although Fuel-injection techniques 9 this is a direct result of the diesel Fuel supply and delivery 12 engine’s better fuel economy. It was Mechanical engine-speed control also possible during the past few years (governing) 22 to considerably lower the particulate Injection timing 29 emissions which are typical for the Add-on modules and diesel engine. shutoff devices 32 The popularity of the high-speed diesel engine in the passenger car though, Testing and calibration 45 would have been impossible without Nozzles and nozzle holders 46 the diesel fuel-injection systems from Bosch. The very high level of precision Electronically-controlled axial- inherent in the distributor pump means piston distributor fuel-injection that it is possible to precisely meter pumps VE-EDC 54 extremely small injection quantities to the engine. And thanks to the special Solenoid-valve-controlled governor installed with the VE-pump in passenger-car applications, the engine axial-piston distributor fuel-injection responds immediately to even the finest pumps VE-MV 60 change in accelerator-pedal setting. All points which contribute to the sophisti- Start-assist systems 62 cated handling qualities of a modern- day 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 distri- butor pump, and how it adapts injected fuel quantity, start-of-injection, and duration of injection to the different engine operating conditions. Combustion in the diesel Combustion in the diesel engine engine Power stroke The diesel engine Following the ignition delay, at the begin- ning of the third stroke the finely atom- Diesel combustion principle ized fuel ignites as a result of auto-igni- The diesel engine is a compression- tion and burns almost completely. The ignition (CI) engine which draws in air cylinder charge heats up even further and compresses it to a very high level. and the cylinder pressure increases With its overall efficiency figure, the diesel again. The energy released by the igni- engine rates as the most efficient com- tion is applied to the piston. bustion engine (CE). Large, slow-running The piston is forced downwards and the models can have efficiency figures of as combustion energy is transformed into much as 50% or even more. mechanical energy. The resulting low fuel consumption, coupled with the low level of pollutants in Exhaust stroke the exhaust gas, all serve to underline In the fourth stroke, the piston moves up the diesel engine’s significance. again and drives out the burnt gases The diesel engine can utilise either the through the open exhaust valve. 4- or 2-stroke principle. In automotive A fresh charge of air is then drawn in applications though, diesels are practi- again and the working cycle repeated. cally always of the 4-stroke type (Figs. 1 and 2). Combustion chambers, Working cycle (4-stroke) turbocharging and In the case of 4-stroke diesel engines, supercharging gas-exchange valves are used to control Both divided and undivided combustion the gas exchange process by opening chambers are used in diesel engines and closing the inlet and exhaust ports. Fig. 1 Principle of the reciprocating piston engine Induction stroke During the first stroke, the downward TDC Top Dead Center, BDC Bottom Dead Center. Vh Stroke volume, VC Compression volume, movement of the piston draws in un- s Piston stroke. throttled air through the open intake valve. VC TDC Compression stroke s During the second stroke, the so-called Vh compression stroke, the air trapped in the BDC cylinder is compressed by the piston which is now moving upwards. Com- pression ratios are between 14:1 and 24:1. In the process, the air heats up to TDC temperatures around 900°C. At the end of the compression stroke the nozzle in- jects fuel into the heated air at pressures BDC 2 of up to 2,000 bar. UMM0001E (prechamber engines and direct-injec- Diesel-engine exhaust The diesel tion engines respectively). emissions engine Direct-injection (DI) engines are more ef- A variety of different combustion deposits ficient and more economical than their are formed when diesel fuel is burnt. prechamber counterparts. For this rea- These reaction products are dependent son, DI engines are used in all commer- upon engine design, engine power out- cial-vehicles and trucks. On the other put, and working load. hand, due to their lower noise level, The complete combustion of the fuel prechamber engines are fitted in passen- leads to major reductions in the forma- ger cars where comfort plays a more im- tion of toxic substances. Complete com- portant role than it does in the commer- bustion is supported by the careful cial-vehicle sector. In addition, the matching of the air-fuel mixture, abso- prechamber diesel engine features con- lute precision in the injection process, siderably lower toxic emissions (HC and and optimum air-fuel mixture turbulence. NOX), and is less costly to produce than In the first place, water (H2O) and carbon the DI engine. The fact though that the dioxide (CO2) are generated. And in rela- prechamber engine uses slightly more tively low concentrations, the following fuel than the DI engine (10...15 %) is substances are also produced: leading to the DI engine coming more and more to the forefront. Compared to – Carbon monoxide (CO), the gasoline engine, both diesel versions – Unburnt hydrocarbons (HC), are more economical especially in the – Nitrogen oxides (NOX), part-load range. – Sulphur dioxide (SO2) and sulphuric acid (H2SO4), as well as Diesel engines are particularly suitable – Soot particles. for use with exhaust-gas turbochargers or mechanical superchargers. Using an When the engine is cold, the exhaust-gas exhaust-gas turbocharger with the diesel constituents which are immediately engine increases not only the power noticeable are the non-oxidized or only yield, and with it the efficiency, but also partly oxidized hydrocarbons which are reduces the combustion noise and the directly visible in the form of white or blue toxic content of the exhaust gas. smoke, and the strongly smelling alde- hydes. Fig. 2 4-stroke diesel engine 1 Induction stroke, 2 Compression stroke, 3 Power stroke, 4 Exhaust stroke. 1234 UMM0013Y 3 Diesel fuel- injection Diesel fuel-injection systems: systems: An overview An overview Fields of application Technical Diesel engines are characterized by their requirements high levels of economic efficiency. This is of particular importance in commercial More and more demands are being made applications. Diesel engines are em- on the diesel engine’s injection system as ployed in a wide range of different ver- a result of the severe regulations govern- sions (Fig. 1 and Table 1), for example as: ing exhaust and noise emissions, and – The drive for mobile electric generators the demand for lower fuel-consumption. (up to approx. 10 kW/cylinder), Basically speaking, depending on the – High-speed engines for passenger particular diesel combustion process cars and light commercial vehicles (up (direct or indirect injection), in order to to approx. 50 kW/cylinder), ensure efficient air/fuel mixture formation, – Engines for construction, agricultural, the injection system must inject the fuel and forestry machinery (up to approx. into the combustion chamber at a pres- 50 kW/cylinder), sure between 350 and 2,050 bar, and the – Engines for heavy trucks, buses, and injected fuel quantity must be metered tractors (up to approx. 80 kW/cylinder), with extreme accuracy. With the diesel – Stationary engines, for instance as engine, load and speed control must take used in emergency generating sets (up place using the injected fuel quantity with- to approx.