THE UNIVERSITY OF NEW SOUTH WALES BOX 1, POST OFFICE, KENSINGTON 26,8.66 WEISS, K. The Effect, of water-injection on the performance of internal combustion engines. Permission to read/ photocopy this thesis has been granted. Mechanical Eng THE EFFECT OF WATER-INJECT I ON ON THE PERFORMANCE OF INTERNAL COMBUSTION ENGINES by K. Weiss, Dipl.Ing. Vienna, A.M.I.E., Aust. A Higher Degree Thesis submitted to the N.S.W. University of Technology. June 1957. 0F NEW KEN5INGTDN a> j Ll BRA^ UNIVERSITY OF N.S.W. 27979 26. FEB.75 LIBRARY (i) SUMMARY To determine the influence of an anti-detonant injection on the performance of an internal combustion engine two methods were adopted: 1. A mathematical approach by which the theoretical drop of combustion temperature was calculated for an Otto cycle using octane as fuel and water as internal coolant, the water being 25% by weight of the fuel. The method derived holds good for any fuel and coolant. 2. An experimental method in which a series of engine tests were carried out using the Ricardo E-6/S variable compression engine with a manually controlled valve to regulate the coolant flow. The main object of this part of the thesis was to determine any improvement in power and economy, when water or water-alcohol at various weight-ratios was used for anti-detonant injections. Observation data, result sheets and performance curves are presented. The graphs are used to analyse test results but may also be used to calculate other values such as per- n ■- centage gain of power if desired*-;Econopy figures are based on 3s./8^/2d* per gal-ion for standard grade V petrol and 7s./Id. per gaXloH "for methylated spirit. (li) From the attached observation and result sheets, variables such as exhaust gas temperature, inlet air temperature and torque values may be plotted. (iii) ACKNOWLEDGMENT. The author is indebted to Mr. S. Smith for his assistance in installing and calibrating the test equip­ ment and for maintaining the Ricardo E-6/S variable com­ pression engine in good working order during the test period. Thanks are also due to Mr. G. Reynolds for his help each day in preparing the engine for testing and for his assistance in taking readings during the test runs. The author is greatly indebted to Mr. J. Grant for drawing the numerous test graphs and to Mr. E.C.Martin, School of Applied Chemistry, who provided data on specific gravity and on heat values of the fuels used. Finally, thanks are due to Mr. H. Baker from S. Smith and Sons (Aust.) Pty. Ltd., who provided the author with special spark plugs, modified to carry thermocouple wires instead of the centre electrode. (iv) CONTENTS CHAPTER PAGE 1 History of Anti-detonant Injection 1 - 8a 2 Influence of Anti-detonant Injection on a Detonating Combustion Process 9-12 3 Theoretical Investigation of the Thermodynamic Effect of Adding an Internal Coolant to an Octane-Air Mixture 13 - 41 4 Laboratory Tests: 4-1. Aim of investigation; 42 4-2. Test equipment and instrumentation; 43 - 60 4-3. Sample calculations; 61 - 66 4-4. Test details; 67 - 77 4-5. Test results; 77 - 106 4-6. Accuracy of test results; 107 - 112 4-7. Internal condition of the engine; 113 - 116 4-8. Reduction in Mean Cycle Temperature when using Water as an Internal Coolant. 116a- 116 d 5 Conclusion. 117 - 121 6 Bibliography. 122 - 125 7 Appendix: 7-1. Observation sheets (tests 5 and 6 only). 126 - 133 7-2. Result sheets (tests 5 and 6 only). 134 - 141 1 CHAPTER 1 HISTORY OF ANTI-DETONANT INJECTION. Water-inject!on as an anti-detonant for internal combustion engines is a fairly old idea and tests had been carried out before 1900 by Benki in Hungary. In 1913, Professor B. Hopkinson^ of the University of Cambridge delivered a paper at a meeting of the Institution of Mechanical Engineers, dealing with his experiences gained when using water as an internal coolant for horizontal gas engines. In this classical report he pointed out that difficulties with engine liners and pistons, resulting from high temperature differences, could be eliminated by the use of water injection. Furthermore, pre-ignition of the fresh charge could be prevented, because the temper­ ature of the combustion chamber walls and of carbon and tar deposits were kept much below that which is necessary to ignite the incoming charge. Hopkinson also found that the maximum cycle pressure was reduced by 100 psi, and the explosion became almost inaudible. Indicator cards taken showed that the reduction in maximum pressure was counter-balanced by a slightly raised expansion line, when compared with diagrams of engines without internal coolant. Professor Hopkinson concluded that, when using water injection, the pressure was better sustained, partly by the formation of steam and partly by the reduction in heat losses, with the result that the indicator cards became fatter and less peaky. To regulate the water flow into the cylinder, a ball-valve was used and a special spray nozzle was fitted into the cylinder-head to direct the water to those parts la of the engine which needed cooling most. So successful was this method that Hopkinson later designed some engines with­ out any external water-jackets. In the middle 20’s a tractor appeared on the market, called ”Rumley Oil Pull Tractor ”, which used kerosene for fuel and water for controlling detonation. At full load, a manually operated needle-valve permitted the entry of just sufficient water to stop detonation, with the result that noiseless running conditions were established. The only drawback to this arrangement was that if resetting of the valve at light load was forgotten, the engine was gradually flooded and trouble from corrosion was experienced. In 1938 E. L. Barger and J. L. Gale carried out a number of tests, using a ’’Hercules 00C *' and a ”McCormick-Peering" engine with water as an internal cool­ ant. Their results may be summed up as follows: *For low octane fuels of high distillation range, the maximum safe load could not be increased because suf­ ficient water to limit detonation could not be injected without dropping the load. However, for low-octane fuels with a low distillation range, the maximum safe load was increased considerably without appreciable sacrifice of thermal efficiency. Medium-octane fuels (23-30 distillate) responded fairly well to water-injection, showing useful power increase.” At the same time it was found that the use of water-injection increased the thermal efficiency only when operating on such a load that detonation without water- injection had a medium intensity. On the other hand, M.S. Kuhring^, who injected water into the air-fuel mixture at the supercharger of a Jaguar MK.IV aircraft engine, found the following results: 2 ”When water was injected at the rate of 83 lb. per 100 lb. of fuel, using a rich mixture, an increase of about 90 B.H.P. was obtained without rise in cylinder temperature and apparent detonation. The specific fuel consumption remained practically constant and quite an appreciable cooling of the air-fuel charge was noted.*’ At the beginning of World War II, two publications appeared, one in Germany by K. Zinner^ and the other in U.S.A. by R. Wiebe, J.F. Shultz and J.F. Porter^. In both papers, a theoretical approach was made to the calculation of engine conditions, when an internal coolant was injected into an engine cylinder. The American team produced two sets of Mollier diagrams, similar in appearance to the thermodynamic charts, calculated by Hershy, Eberhardt and Hottel. The Mollier diagrams were derived for a chemically correct ethyl- alcohol-air mixture and for a chemically correct octane-air mixture plus water, the latter injected at the rate of 35 lbs. per 100 lbs. of fuel. During World War II, water and water alcohol in­ jections were used with great success on supercharged air­ craft engines to increase internal cooling at taking-off and at maximum flight speed. Intensive research was carried out by a number of people at various laboratories in the U.S.A. and in Great Britain, and most of the results were published in various N.A.C.A. wartime reports. The National Research Laboratory of Ottawa, for instance, used a supercharged Armstrong Siddeley Jaguar MK.IV engine. The water for injection was fed from the City main under pressure, passed through a calibrated orifice plate, and then through a copper tube into a distance piece between the supercharger and the carburettor. The water, travelling at high speed, was atomized when 2a leaving the tube while "being drawn into the supercharger impeller. Water, in this case, not only suppressed detonation hut provided intercooling of the intake air by evaporation of the liquid in the supercharger. At the same time, R.J. Koenig and G. Heiser^ studied the effect of water injection on the cooling characteristics of a Pratt and Whitney R 2800 aircraft engine, while T.D. Wear^ and his team investigated the effect of various internal coolants on knock-limited and temperature-limited power of aircraft engines. A.H. Bell^) wrote another paper, dealing with the continuous use of internal coolants to suppress knock in aircraft engines, cruising at high power. E.W. Steinitz^Q^, who also studied the influence of water injection on the performance of aircraft engines pointed out that the use of water as an anti-detonant, with its attendant equipment, complicates the engine and increases the total weight of the aircraft. Danger also exists that the water may freeze unless mixed with an anti-freeze solution.