Cleaner Jags

Press, 21 July 1978, Page 14

Cleaner Jags

The latest versions of sixcylinder 4.2 litre XJ Jaguar saloons bound for North America are cleaner, faster and more economical.

They are equipped with the latest anti-pollution technology, using Lucas/ Bosch L-jetronic fuel injection with feedback control from an exhaust sensor and a three-way catalytic exhaust converter. This development is a significant advance by Jaguar engineers, enabling the car to meet the stringent California clean-air laws without such sideeffects on performance and fuel thirst commonly associated with earlier “detoxing” methods. Because the new system works so well, Jaguar is offering it to Americans outside California, in spite of the fact that the Federal pollution regulations are less demanding.

The most important element in the new Jaguar system is the use of the three-way catalyst in the exhaust system. This oxidises hydrocarbons and carbon monoxide and simul-

taneously reduces the nitric oxides. Hence the three unwanted pollutants are largely transformed into harmless water, carbon dioxide and nitrogen. The three-way catalyst can only work efficiently if the gases entering it have been generated by an engine burning fuel and air in ideal proportion. Tiny variations of the air-fuel ratio can stop the catalyst from working properly. Even the most precise conventional fuel injection system allows variations many times greater than those which can be tolerated, so a special control was needed. This control uses the principle of a closed-loop feed-back from an exhaust sensor placed between the engine and the catalyst. By generating an electrical signal in proportion to the free oxygen in the exhaust gases, the sensor tells the injection control unit whether the mixture is too rich or too lean for the catalyst to work, and the fuelling is adjusted accordingly.