Exhaust pulse pressure charging (EPPC) is a system for

supercharging In an internal combustion engine, a supercharger compresses the intake gas, forcing more air into the engine in order to produce more power for a given displacement. The current categorisation is that a supercharger is a form of forced induc ...

two-stroke A two-stroke (or two-stroke cycle) engine is a type of internal combustion engine that completes a power cycle with two strokes (up and down movements) of the piston during one power cycle, this power cycle being completed in one revolution of ...

diesel engine The diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression; thus, the diesel engine is a so-ca ...

s of the loop-scavenge type. Loop-scavenge engines cannot be pressure-charged in the same way as uniflow engines or four-stroke engines because the inlet and exhaust ports are open at the same time.

Overview

The engine usually has a

Roots blower The Roots-type blower is a positive displacement lobe pump which operates by pumping a fluid with a pair of meshing lobes resembling a set of stretched gears. Fluid is trapped in pockets surrounding the lobes and carried from the intake si ...

to provide air for scavenging and this is arranged to deliver excess air so that air follows the exhaust gases into the exhaust manifold. Some of this air is then forced back into the cylinder by a rise in pressure in the exhaust manifold resulting from the exhaust pulse from another cylinder. For additional pressure charging a

turbocharger In an internal combustion engine, a turbocharger (often called a turbo) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake gas, forcing more air into the engine in order to pro ...

may be fitted, in series with the Roots blower, but a turbocharger cannot be used alone because it would not provide enough air for scavenging at low speeds.

Exhaust Pulse Pressure Charging Advantages and Disadvantages

Pulse pressure charging is much more effective with a low load and at low speed than traditional supercharging since the exhaust is coming from engine cylinders instead of the engine as a whole. Pulse pressure charging remains efficient even when the break mean effective pressure (BMEP) is below 8 bar. Additionally, the exhaust pipes used in pulse pressure charging have a smaller diameter, so the pressure in the system builds much faster. Pulse pressure charging does not require an auxiliary scavenger pump and blower as the load on the motor changes and it provides a lot of energy available at the turbine, allowing for good supercharger acceleration. However, since the exhaust comes in pulses from the cylinders, the exhaust piping is much more complicated in a pulse pressure system because it is dependent on the number of cylinders and their firing order. In some cases, exhaust pipes must be different sizes to keep the overall pressure as consistent as possible. Finally, high pressure exhaust from one cylinder can occasionally pass back into another cylinder during its scavenging period while it is at low pressure which has a negative impact on the efficiency of the combustion in the cylinder.

Applications

Exhaust pulse pressure charging is generally used in very large machines with auxiliary diesel engines, such generators. In large pieces of machinery, such as boats and locomotives, the main engine tends to be under a high and constant load meaning a constant pressure charging system is much more efficient. An auxiliary engine, such as a generator, is much more likely to experience variation in load so exhaust pulse pressure charging is more efficient. Additionally, since pulse pressure charging remains efficient even at low break mean effective pressure, an auxiliary engine with pulse pressure charging is capable of producing a large amount of power even when the full capability of the engine is not being utilized.

Examples

Exhaust pulse pressure charging was used by

Crossley Crossley, based in Manchester, United Kingdom, was a pioneering company in the production of internal combustion engines. Since 1988 it has been part of the Rolls-Royce Power Engineering group. More than 100,000 Crossley oil and gas engines ...

in these diesel locomotive engines: * the HST-Vee 8, used in the

British Rail Class 28 The British Rail Class 28 ( Metro-Vick Type 2) diesel-electric locomotives, known variously as 'Metrovicks', 'Crossleys' or 'Co-Bos', were built under the Pilot Scheme for diesel locomotives as part of the British Railways 1955 Modernisation P ...

, the

CIE 001 Class The Córas Iompair Éireann 001 Class locomotive was manufactured by Metropolitan-Vickers at their Dukinfield Works in Manchester. The 001 Class locomotive was the backbone of mainline passenger and freight train services on the Irish railway ...

and the

WAGR X class The X Class were a class of diesel locomotive built by Beyer, Peacock & Company and Metropolitan-Vickers, Bowesfield Works, Stockton-on-Tees for the Western Australian Government Railways between 1954 and 1956. Construction In the early 195 ...

* the EST-Vee 8 used in the

CIE 201 Class The Córas Iompair Éireann 201 Class was a class of 34 diesel electric locomotives manufactured by Metropolitan-Vickers at their Dukinfield Works in Manchester. They were a smaller, lighter and less powerful version of the 001 Class and were ...

* the ESNT 6 used in

British Rail Class D3/3 British Rail Class D3/3 was a 0-6-0 shunting locomotive built by British Rail at their Derby Works in England. It was similar to the British Rail Class 08, except they were built with different engines and traction motors. They were all withdra ...

shunting locomotives

References

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