Experiments on Two-Stroke Engine Exhaust Ports under Steady and Unsteady Flow Conditions

Abstract

A theoretical and experimental study of the discharge from an engine cylinder to atmosphere was made. The objective of the work was to establish suitable data for the design of exhaust ports. Two theoretical methods were used, in the first method the discharge was analysed by the method of characteristics and it was shown that the discharge was by wave action. The second method neglected the particle velocity in the cylinder. Comparison of the latter method with the solution by characteristics showed good agreement over the main part of the discharge and it was possible by that method to develop a simple design formula for the estimation of the port area.

The experimental investigation was carried out on a special machine which simulated in all respects the exhaust-port arrangement of a two-stroke cycle engine. The machine was designed to investigate the effect of port configuration, port timing, cylinder length, engine speed, release pressure, and temperature. By suitably arranging the variables in non- dimensional groups a wide range of engines could be simulated. The flow characteristics of the exhaust ports were examined under both steady and unsteady flow conditions. The following conclusions were drawn: (1) the coefficient of discharge for the exhaust ports increased with cylinder pressure and decreased with increased port area, (2) the coefficient of discharge was lower under dynamic conditions than under steady flow conditions, (3) the dynamic coefficient of discharge decreased with reduction in cylinder length at release, (4) the effect of early port opening was to reduce the blowdown time, (5) the effect of piston movement during discharge was to reduce the effective port area required.

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References

Benson

R. S.

1954 Univ. Lond. M.Sc. (Eng.) Dissertation, ‘The Flow of Gases in Large Two Cycle Diesel Engines’.

List

Reyl

1949 ‘Der Ladungswechsel der Verbrennungskraft-machine’ (Springer-Verlag, Vienna).

Minkhorst

J. H.

1952 Poly. Tijdschr., p. 706a, ‘Berunchnung van de tijddroftakt nadiz wir de uitlaat bij tweitaktdiesel motore’.

Purday

H. F. P.

1937 ‘Diesel Engine Design’, (Constable and Co., London).

Schweitzer

P. H.

1949 ‘Scavenging of Two-Stroke Diesel Engines’ (Macmillan and Co. Ltd, London).

Weaving

J. H.

1949 Proc. Instn mech. Engrs, Lond., vol. 161, p. 98, ‘Discharge of Exhaust Gases in Two-stroke Cycle Engines’.

Wallace

F. J.

Mitchell

R. W. S.

1953 Proc. Instn mech. Engrs, Lond., B, vol. 1B, p. 343, ‘Wave Action Following Sudden Release of Air Through an Engine Port System’.

Cole

B. N.

Mills

1953 Proc. Instn mech. Engrs, Lond., B, vol. 1B, p. 364, ‘Theory of Sudden Enlargements Applied to the Poppet Exhaust Valve with Special Reference to Exhaust Pulse Scavenging’.

Wallace

F. J.

Nassif

M. H.

1954 Proc. Instn mech. Engrs, Lond., vol. 168, p. 515, ‘Air Flow in a Naturally Aspirated Two-stroke Engine'. (10) Jenny, E. 1949 E.T.H.Z. Zurich (Doctor's Thesis), ‘Berechnungen und Modelversuche uber Druckenwellen Grosser Amplituden in Auspuff-Leitungen', (11) Benson, R. S. 1955a Engineer, Lond., vol. 199, p. 546, ‘Discharge of Gas from Cylinder to Atmosphere'. Benson, R. S. 1955b J. R. Aero. Soc., vol. 59, p. 773, ‘The Effect of Excess Scavenge Air on the Pressure Drop in the Cylinder of a Two Stroke Cycle Engine During Exhaust Blowdown'. (12) Pounder, C. C. 1957 Trans. Inst. mar. Engrs, vol. 69, p. 161, ‘The Harland and Wolff Pressure Charged Two-Stroke Single-Acting Engine’.

10.

Giffen

1940 Engineering, Lond., vol. 150, p. 134, ‘Rapid Discharge of Gas from a Vessel into the Atmosphere’.

11.

Benson

R. S.

1951 Brit. Shipb. Res. Ass. Report No. 73, ‘Analysis of Light Spring Diagrams from a Five Cylinder Doxford Engine with Single Crank-Driven Scavenge Pump’.

12.

Benson

R. S.

1957 Engineer, Lond., vol. 203, p. 946, ‘Discharge from an Engine Cylinder to Atmosphere’.

13.

Roach

W. J. R.

Hempson

J. G. G.

1952 Engineer, Lond., vol. 194, p. 7, ‘A Modified Farnboro Electric Indicator’.

14.

Roach

W. J. R.

Hempson

J. G. G.

1954 Brit. Shipb. Res. Ass. Report No. 130, ‘Further Modifications to the Farnboro Electric Indicator to Provide Multichannel Indication and Improved Low-Pressure Recording’.

15.

Benson

R. S.

1957 J. R. Aero. Soc., vol. 61, p. 127, ‘A Method for Calculating the Exhaust-Port Area for TwoStroke Cycle Engines’.

16.

Benson

R. S.

1958 J. R. Aero. Soc., vol. 62, p. 382, ‘The Effect of Variation in Cylinder Length on the Exhaust Port Timing of a Two-Stroke Cycle Engine’.

17.

Sauer

1947 Minist. Supply Theoret. Res., Translation 1/47, ‘Non-Stationary Problems of Gas Dynamics (Pressure Waves of Large Amplitude)’.

18.

Shapiro

A. H.

1954 ‘The Dynamics and Thermodynamics of Compressible Fluid Flow’ (Ronald Press Co., New York).

19.

Benson

R. S.

1957 Trans. Liverpool Engng Soc., vol. 76, p. 88, ‘The Application of Modern Gas-Dynamic Theories to Exhaust Systems of Internal Combustion Engines’.

20.

Stanton

T. E.

1926 Proc. roy. Soc., vol. 111, p. 306, ‘On the Flow of Gases at High Speeds’.

21.

Chaplygin

S. A.

1904 Sci. Annals. Imp. Univ. Moscow Phys.-Math., Div. 21, ‘On Gas Jets’.

22.

Chaplygin

S. A.

1944 Nat, adv. Comm. Aero., T.M. No. 1063, ‘On Gas Jets’.

23.

List

1953–54 Proc. Auto. Div., Instn mech. Engrs, p. 45, ‘The Charging Process of Internal-combustion Engines, With Special Reference to the Two-stroke Cycle’.

24.

Jobson

D. A.

1955 Proc. Instn mech. Engrs, Lond. vol. 169, p. 767, ‘On the Flow of a Compressible Fluid Through Orifices’.

25.

Rudinger

1955 J. appl. Phys., vol. 26, p. 981, ‘On the Reflection of Shock Waves from an Open End of a Duct’.

26.

Rudinger

1957 J. Fluid Mech., vol. 3, p. 48, ‘The Reflection of Pressure Waves of Finite Amplitude from an Open End of a Duct’.

27.

Jackson

1956 Trans. Inst. mar. Engrs, vol. 68, p. 373, ‘Recent Developments in Marine Diesels (Doxford Engine)’.

28.

Withers

J. G.

1955 Engineer, Lond., vol. 200, p. 860, ‘Effects of Indicator Passages on the Accuracy of Indicator Diagrams’.