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The fast injection gospel according to Cummins

14th July 1984, Page 52
14th July 1984
Page 52
Page 53
Page 52, 14th July 1984 — The fast injection gospel according to Cummins
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Improved fuel efficiency, cleaner exhaust and reduced noise levels are the major benefits achieved directly or indirectly by Cummins with its range of fast injection "Big Cam" engines.

THE BIG CAM concept was first used by Cummins in the UK with the introduction of the E290 engine back in 1978. With Cummins's mechanically actuated PT fuel system the company had gained a reputation for a reliable and durable product which differed in concept to a major degree from conventional 'jerk' pump systems. In the late '70s' Cummins engines shared the same reputation as the fuel system, ie that of high durability and reliability. However, the product was not considered to be one of the most economical high horsepower cv engines. Operators in that period specified Cummins power because of its capability of covering very high mileages reliably.


When fuel cost under £1 a gallon, economy, while important, was not the priority it is today. The 1973 oil crisis changed all that and the steadily increasing spiral of fuel costs from then on convinced Cummins that its product had to compete with the best available engines on all scores — including economy.

Driven on by the rise in fuel prices, Cummins engineers were also influenced by other demands. In 1972 the US Environmental Protection Agency issued a directive that the emissions level for automotive engines in use in America should not exceed 5 grams bhp/hr of NOX and HC. In addition the directive also stated that exhaust smoke capacity should not exceed 15 Hartridge units (2.2 Bosch units). Then, these figures seemed impossible to match, indeed with the benefit of several years research the goals set by this directive would be hard to meet. However, the directive never, in fact, entered the statute book.

But Cummins main research and engineering facility in Columbus, Indiana, embarked on a dovetailed investigation to match Cummins products to the tough requirements of the directive. Then, as now, the high horsepower Cummins product line used the mechanically actuated PT system. PT is an abbreviation for pressure time, a description of the system which uses a pump to supply fuel at low pressure to the injector through internal fuel lines. The injector is mechanically actuated via push rods actuated by an additional lobe on the camshaft. This creates the high pressure required to form the fine spray for efficient combustion.


Retarding the timing limits peak temperature, and hence controls the formation of oxides of nitrogen (NOX). To improve fuel economy and reduce the unburnt hydrocarbons the combination of faster injection and shorter injection duration resulted in more efficient combustion. Accordingly Cummins's initial research work was centred on the size of the camshaft where the injector cam lobe is located. It was considered that research in this area would allow modifications to be made to the fuel injection characteristics to achieve the requirements to improve economy and reduce emissions.

The existing camshaft, used then on all Cummins automotive engines, had 2-inch diameter journals. The Columbus r and d effort evaluated camshafts up to 3 inches in diameter taking 0.125 inch increments.

This research established that a camshaft with a cam journal diameter of 2.5in could meet the projected legislation, with minimal changes to the existing 14-litre cylinder block. The engine was introduced to the US truck market during 1976 and offered a 6 per cent fuel economy benefit over preceding small cam 14-litre Cummins engines. During the same year Cummins European marketing and engineering groups expressed a major interest in the Big Cam concept. Then, as now, there was no formal legislation on diesel exhaust emissions for European markets. However, the fuel economy benefits offered by the Big Cam engine were very attractive. In addition it was con sidered that a European specification would gain by additional fuel economy benefit, as a direct result of a trade off against emissions.

For Europe

Thus a joint design and development programme was undertaken in mid 1976. Cummins' European technical centre and manufacturing facilities cooperated with the objective of creating a fuel efficient, high power engine for European transport.

The result of this work was launched in Europe in 1978 as the Formula E290. It retained all the features of the US Big Cam engine with various other engineering changes to tailor it to European needs.

Both the European and US specification Big Cam engines pioneered the use of fast, very high pressure injection systems. Before the introduction of the Big Cam engine Cummins had been using injection pressures of around 11,000 psi. With the introduction of the bigger camshaft, injection pressures of 14,000 psi were achieved.

Since the introduction of the E series engine in 1978, there have been no serious operational problems associated with these very high injection pressures. In part, this is due to the PT fuel system's characteristic of confining high injection pressures solely to the injector nozzle area.

To take advantage of this higher pressure injection, which results in a given amount of fuel being injected in a shorter period, the Big Cam engine has an injection period which is shorter by some 12 degrees than its small cam predecessor. By reducing the injection period the amount of crank angle available for combustion and expansion is increased and thus more efficient use of the fuel is achieved.

Also with the Big Cam engines the injection timing is retarded so that is starts later in the cycle to reduce exhaust emission levels. By retarding injection timing the fuel can be injected into hotter compressed air in the cylinder, reducing both noise and vibration. Higher pressure injection in a shorter period of the crank angle allows a more complete combustion and hence improved fuel efficiency.

More power

The E290 engine has demonstrated these characteristics since its introduction. Fast injection and other associated engineering changes, incorporated into the unit made it noticeably quieter than its turbocharged predecessors. Additionally, exhaust smoke levels were considerably reduced compared with any previous Cummins engine and comfortably met all current and proposed European requirements for this characteristic.

Since the E290's introduction Cummins has applied the Big Cam technique to the bulk of its automotive engines offered for sale in the UK. The E290 was swiftly followed by higher power, charge-cooled derivatives which took the Big Cam E series range up to 400 bhp gross.

The Big Cam technique was also applied to the company's Darlington-built small-vee range of high speed diesels. Again the Big Cam gave fuel economy, noise and emissions benefits to these smaller 8.3 and 9.1 litre units.

Ten litre

In all these instances the Big Cam and its associated fast injection has been introduced to existing engines which were upgraded. Cummins has also incorporated the same concept in an engine at its design stage.

This was the Ten Litre, which has an even greater camshaft diameter than that used in the small-vee and 14 Litre engines.

Since the Ten Litre's introduction the Big Cam concept has been widely proven by all classes of vehicle operator. Whereas the 14 litre engine was widely available in maximum weight tractive units, its usage in multi-wheeler rigids was restricted. The lightweight Ten Litre engine allows Cummins to corn

pete in a much wider segment of the cv market. It has seen the company enter the passenger vehicle market, in a major way, for the first time.

The Ten Litre's success owes a lot to the Big Cam, fast injection characteristics which have been applied to this unit. Injection pressures are higher than those employed in the 14 litre engine. With the Ten Litre, pressures of up to 20,000 psi are achieved. Again the PT fuel system is used and the engine's economy reflects the advantages of shorter, faster injection.

Super E

With the launch earlier this year of the Super E Series range Cummins has further refined the fast-injection concept. The new high power 14 Litre Cummins engines use what the company designates a Hi-lift Big Cam. This has modified the fast, high injection pressures used in the Cummins 14 Litre.

As a result of these and other changes the Super E engihes give even better economy than their after-cooled E Series predecessors. In addition a further noise reduction of 1.5 dB{A} has been achieved through these Super E combustion refinements.


Locations: Columbus

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