Scholars' Mine Masters Theses Student Theses and Dissertations 1949 Water injection in the modern automotive spark ignition engine Leonard Carl Nelson Follow this and additional works at: https://scholarsmine.mst.edu/masters_theses Part of the Mechanical Engineering Commons Department: Recommended Citation Nelson, Leonard Carl, "Water injection in the modern automotive spark ignition engine" (1949). Masters Theses. 6801. https://scholarsmine.mst.edu/masters_theses/6801 This thesis is brought to you by Scholars' Mine, a service of the Missouri S&T Library and Learning Resources. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. i WATER INJECTION IN THE MODERN AUTOMOTIVE SPARK IGNITION ENGINE BY LEONARD C. NELSON A THESIS submitted to the faculty of the SCHOOL OF MINES AND METALLURGY OF THE UNIVERSITY OF MISSOURI in partial fulfillment of the work required for the Degree of MASTER OF SCIENCE, MElJHANICAL ENGINEERING MAJOR Rolla, Missouri 1949 1i ACKNONLEDGEMENTS The author is indebted to Dr. A. J. Miles for his guidance and timely suggestions during the course of this investigation, and t. the students who assisted in oonducting the tests. iii CONTENTS Page Acknowledgements ••••••••••••••••••••••• ii List of illustrations•••••••••••••••••• iT List of tables•••.••.•••••••••••••••••• T List of plates (graphs)•••••••••••••••• vi PART I Introduction•• ~ .••••••••••••••••••••••• 1 PART II Teat equipment .••.•••.••.•.••••.••••••• 6 PART III Test procedure••••••••••••••••••••••••• 9 PART IV Interpretation of test results••••••••• 14 PART V Conclusions •.•.••.••...•...•.....•..••. 42 Bibliography•••.••••••••••••••••••••••• 43 Vita............••.•......•..........•. 44 iT LIST OF ILLUSTRATIONS rig. Page 1. Photograph of test equipment••••••••••••••••••••••••••••• 12 2. Photograph of water injection system••••••••••••••••••••• 13 v LIST OF TABLES Table No. Page 1. Performance data for aviation gasoline••••••••••••••• 18 2. Performance data tor regular gasoline (J) •••••••••••• 20 3· Performance data for regular gasoline (A) •••..••••••• 22 4. Performance data for regular gasoline (B) •••••••••••• 24 5. Performance data for regular gasoline eC) •••••••••••• 26 6. Performance data for regular gasoline (D) •••••••••••• 28 1- Performance data tor regular gasoline (E) •••••••••••• 30 8. Performance data for regular gasoline (F) •••••••••••• 32 9- Performance data for regular gasoline eG) •••••••••••• 34 10. Performance data for regular gasoline (H) •••.•••••••• 36 11. Pertormance data for regular gasoline (I)•••...•.•.•• 38 12. Performance data tor regular gasoline (J)••...••••.•• 40 vi LIST OF PLATES Plate No. Page 1. Octane utilization•••••••••••••••••••••••••••••••••••• 11 2. Performance curves (87 octane gasoline)••••••••••••••• 19 3· Performance curves for regular gasoline (J) •••.••••••• 21 4. Performance curves for regular gasoline (A) ••••••••••• 23 5. Performance curves for regular gasoline (B) ••••••••••• 25 6. Performance curves for regular gasoline (C) ••••••••••• 27 7. Performance curves for regular gasoline (D) ••••••••••• 29 8. Performance curves for regular gasoline (E) ••••••••••• 31 9. Performanoe curves for regular gasoline (F) ••••••••••• 33 10. Performance curves for regular gasoline (G) ••..•..•..• 35' 11. Performance curves tor regular gasoline (H) ••••••••••• 31 12. Performance curves tor regular gasoline (I)••••••••••• 39 13. Performance curves for regular gasoline (J) ••••••.••.• 41 PART I INTRODUC TI ON 1 The injecti.on of water in the spark igniti.on engine is not new. The effect of humidity in the air on the performance of the spark ignition engine probably initiated the early investigations. The water vapor in the inlet air decreases the speed of the flame front and necessitates spark advance to assure maximum power and maximum efficiency. Water par­ ticles in the air evaporate during the compressi0n and combustion of the inducted charge and decrease the tendency of the engine to detonate. These effects are very evident when operating the spark ignition engine in a moist atmosphere. Water is not a foreign element to the internal combustion engine. It can be easily shown that when one pound of a hydrocarbon fuel burns more than one pound of water is formed in the combustion chamber. The average Hie molar ratio of all the hydrocarbons making up a gasoline is approximately 2.12. On the basis of complete combustion, the end pro­ ducts will be carbon dioxide and water. Balancing the chemical equation we have~ (l) Thus 1 mol of fuel forrr~ 1.06 mola of water. On a weight basis this is 1.125 pounds of water per pound of fuel. This combustion water and any injected water becomes superheated and passes out with the other exhaust products as a vapor. The fundamental reason for injecting water is to suppress ~onation. The exact nature as to how this is accomplished is not definitely known, but it is reasoned that the effect is due to the high heat of vaporization 2 of the water. Detonation, according to Ricardo,(l) results from auto- (1) H. R. Ricardo and H. S. Glyde, The High Speed Internal Combustion Engine, pp. 40-69. ignition of the last part of the charge to burn. Combustion originates normally at the electrodes of the spark plugs. The flame front of the burning progresses across the combustion chamber at rates varying from 40 to 100 it/sec. The rate is a function of these folloWing variables: fuel air ratio, initial pressure, initial temperature, residual gases, humidity, engine speed, compression ratio, and fuel composition. The high specific volume of the burned products tends to compress the mix- ture ahead of the flame front. As a result 'of the compression, the temperature of the unburned charge is raised. If the temperature of the unburned charge is raised above its self-ignition temperature, the entire unburned charge will spontaneously ignite. Once a fuel reaches its self-ignition temperature, a certain amount of time elapses before ignition takes place. The delay period is a function of the fuel com- position, fuel air ratio, and temperature. Although the fuel is above its self-ignition temperature, this delay period may allow the flame to pass through the unburned charge without detonation taking place. If the water acts only as a coolant, then water should affect all gasolines, with the same octane number, alike. When the water is inducted into the cylinder in a vapor state, it reduces the volumetric efficiency of the engine considerably. The specific volume or the vapor at 800r is 30,000 times as great as the specific vol- ume ot the liquid. If the water inducted is in the vapor state, it pro- vides no cooling, and hence no adTSntage can be claimed. The heat from 3 the charge necessary to vaporiz. the liquid water that is taken into the cylinder becomes unavailable since the temperature of the gases on the expansion stroke never drope below the condensation temperature of the water. The work from the superheated steam that forms from the heat exchange between the hot gases and the water caD not be equivalent to the work from the combustion products due to the irreversibility of the heat exchange process. With the aboTe in mind, it is evident that water or water vapor inducted into the engine will lower the output of the engine if the fuel air ratio, compression ratio, or spark advance re- mains the same. Detonation in a spark ignition engine can be controlled by varying the fuel air ratiG. At the beet power mixture the tendency to detonate is the greatest. MOst aircraft engines control detonation by increasing the fuel air ratio (rich mixture). Decreasing the fuel air ratio (lean mixture) would arrive at the same results with more economy but because a lean mixture burns slowly, the engine would tend to heat. To develop the War Emergency Power Rating established by the Army and Navy for the military aircraft without water injectioJl, it was necessary to enrich the mixture beyond "best power mixture" to supress detonatien. With water injectian the mixture could b. leaned t~ the "best power mixture," re- sulting in 8 gain over that power developed using the rieh mixture with­ out water injecti~n.(2) (2) Paul F. Adair, Low Octane Fuel Plus Water Equals High Engine Per­ formance, Aviation Maintenance, Vol. 1, pp. 43-45, February, 1944. Detonation can be controlled by reducing the compression ratio. 4 Lower compression ratios result in lower temperatures after compression, and also lower temperatures of the last part of the charge to burn. This in turn increases the ignition lag and allows normal combustion to take place. The equation for the efficiency of the theoretical spark ignition Otto engine is 1 N =1 - (2) r k _ 1 where r =compression ratio k =adiabatic coefficient It is evident that reducing the compression ratio cuts down on the .f- ficiency of the engine and the work output. Water injection will allow the use of the higher cODlpression ratio with a corresponding increase in efficiency. In the automobile engine today detonation is controlled to a great extent by spark timing. The compression ratio is considerably greater than that ratio which would allow the correct spark advance for maximum power using the regular fuels available. Hence, at full throttle the engine operates at a reduced spark. Water injection allows the spark to be advanced to the optimum position. Thus, more power, better economy, and cooler exhaust valves result. Mr. Wm. M. Holliday's tests(3) on a 1948 car with a compression ratio (3) Wm. U. Holliday, Progress Report on the Duel-Fuel System, S.A.E. Paper, June 6-11, 1948. of 7.0 to 1 shows that even under adverse conditione the engine could have been operating 80 per cent of the time knock-free with a 50 octane fuel. Hence, it is an economic waste to use high octane fuel during this 80 per cent of the time. Water injection is one of the answers to the solution of thi5 problem. Properly injected water could raise the octane number about 15 octane numbers (a solution of yater, alcohol and tetra- ethyl lead could raise the octane number as high 8S 34 octane numbers).