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The New 1,9 L Tdi Diesel Engine With Low Fuel Consumption and Low Emission From Volkswagen and Audi
Published May 14, 1992 by Societe des Ingenieurs de l'Automobile in France
The increasing importance of environmental problems is forcing the automobile manufactures to develop engine concepts that, above all, are distinguished by low fuel consumption and low exhaust pollutant emissions. At Volkswagen, a turbocharged 1.9 ltr. diesel engine with direct fuel injection by way of an electronically controlled system, and regulated exhaust gas recirculation and also an oxidation filter has been developed for use in passenger cars. Here, for the first time ever, a direct injection engine has undercut the exhaust limits prescribed in appendix XXIII.
The working process of the 1.9 ltr. TDI engine has been tuned with regard to low specific consumption, low emissions, high torque at low soot emissions and low noise level.
This paper discusses the operations necessary to optimize the combustion chamber, swirl, fuel injection, turbocharging system and drive train.
On the basis of preliminary examinations the combustion chamber design was the subject of further detailed development with regard to low dead volume and a compression ratio favorable to emissions and noise. An intake port was applied which possesses very good flow characteristics at the required swirl level.
A further developed distributor type fuel injection pump with pressure equalizing valves and return flow restrictor enabled, in conjunction with five-hole injectors, the high injection pressures required for the direct injection combustion process to be obtained. The electronic mapping controls the injection timing and fueling levels resulting in a good basis necessary to meet the strict emission limits. Added to this map controlling the exhaust gas recirculation system was introduced, which reduced the nitric oxide emissions to the required level. An oxidation catalyst is employed for further pollutant reduction. The high degree of torque at a low level of soot emissions was attained by way of an optimized turbocharger, in conjunction with electronic boost pressure control and inter-cooling.
The high torque, even at low engine speeds, and the high cylinder peak pressures cause a high degree of dynamic stress to the power unit. For this reason, the constant load capability of the individual components was adapted to the high stresses with the aid of newly introduced peak loading and component tests as well as with Weibul and Wöhler examinations. Material variants subjected to stresses and their capability to withstand stress were tested and statistically examined in many test series. The results of these tests were for example, special parameter optimization of the crankshaft radii, the designing of the front crankshaft spigot and localized strengthening of the crankcase. When the pistons were designed, attention was not only paid to the high gas forces but also the high thermal load brought about by the combustion chamber recess in the piston crown. The long engine service life shows that the endeavors were a success. The camshaft, fuel injection pump and oil pump are timed and driven by a toothed belt. The high torque peaks of the fuel injection pump drive places in particular an extremely high strain on the toothed belt, in this connection, the main causes of failure were thereby analyzed by way of intensive fundamental investigation, and solutions were evolved by strength-increasing and stress- related measures. Sub assemblies are driven by a Poly-V-belt.