Modern automotive diesels

THIS IS the first of a two part article looking at some developments in diesel vehicle technology that will continue to be significant for years to come. Although the first part will concentrate on passenger car diesel engines, it is impossible to separate their development from that of commercial vehicle engines - each has benefited from developments in the other, particularly in the last quarter century.

Early passenger car diesels were heavy engines fitted to larger cars and often used in taxis where their poor vehicular performance was not as important as their miserly fuel consumption. An Indian example would be the Matador engine used in many "conversions".

First introduced in the mid-1930s, the performance of passenger car diesel engines did not show much improvement until the commercial introduction of the 1.5 litre IDI (indirect injection) engine by Volkswagen in the mid-1970s. The engine was fitted to the Golf (Rabbit in the U.S.) and took the industry by storm. This milestone in engine development was really the derivative of a petrol engine with an aluminium head on a cast iron block. It weighed little more than its cousin and used a toothed belt to drive both its overhead camshaft and its distributor-type fuel injection pump.

Importantly, this engine was manufactured on the same "line" as its cousin and had a specific power output of about 25 kW (about 34 HP) per litre. In comparison, most of its contemporaries could only boast of 20 kW, or less, under rated (standard) conditions. In its relatively light VW Golf home, it offered good performance combined with excellent fuel economy at an affordable price. The French manufacturers, Peugeot-Citroen and Renault, were quick to follow with some excellent diesel vehicles in the 1980s.

The next important step was the introduction of turbochargers to passenger car diesels. Mercedes-Benz, Peu- geot and Volkswagen were the pioneers in this regard, but here, again, VW introduced the most successful package on the Golf while the others used turbos only on their high-end vehicles.

The most rapid development in passenger car diesel technology, however, has occurred in the last dozen years when almost every major manufacturer has introduced vehicles with diesel engines. Engine families which include both petrol (gasoline) and diesel variants have become the standard approach, if not the rule, allowing both types of engines to be produced with the same manufacturing equipment and to be easily adapted to changing customer demands.

The only exception has been Honda which plans to make up for lost time with an Isuzu sourced engine next year. The Honda approach is representative of a new trend and of a cooperative approach rather different from the bitter rivalries of the not-so-distant past. Another example is the joint venture between Ford and Peugeot to jointly develop and manufacture a range of diesel engines at the former Ford car factory at Dagenham, England. It appears that Peugeot will take the lead for the smaller engines with Ford having major responsibility for the other end.

The recent announcement that Hyundai will source car engines from the independent Italian diesel specialist VM Motori (scooped in last week's column), is an indication of practices common in the commercial heavy vehicle industry. Cummins and Caterpillar have long been the kings in this area with Caterpillar's acquisition of Perkins likely to accelerate this trend. Ford and Navistar (formerly International Harvester) have just announced a joint venture to manufacture diesel engines in Mexico while Ford will also source engines from a Brazilian manufacturer.

In addition to turbochargeing, the 1990s saw the widespread adoption of many new features such as intercooling, exhaust gas recirculation (EGR), multi valve cylinder heads and diesel oxidation catalysts. Direct injection (DI) technology and electronic injection control were very important introductions. Compared to good IDI engines with swirl or prechambers, DI engines offer a 15 to 20 per cent reduction in fuel consumption. Combined with electronic injection control and high pressure common rail or unit injector systems, DI technology also means lower pollution levels, higher specific outputs and, more importantly, much higher torque outputs over a wide range of engine speeds, but that is the stuff of the next Motoring Matters.....

C. Manmohan Reddy

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