Water Injection
06-01-2004, 01:25 AM
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Water Injection
At
http://www.carrollsupercharging.com/oldsite/index2.html
I found an interesting little tidbit..
We all have a tendency when we discover such phenomenon and the solution to it, to think we have "invented the wheel." This problem, for one, has been around a long time and Ricardo not only faced it but ran a series of tests in the early 1930's, plotted in the figure above, Reference: The High-Speed Internal Combustion Engine by H. Ricardo. To quote Mr. Ricardo, "In this case, running throughout at a speed of 2,500 RPM and with a compression ratio of 7:1, the engine was run on an economical mixture, i.e. about 10% weak, and supercharge applied to the first incidence of detonation, which occurred when the BMEP had reached 168 pounds per square inch. The mixture strength was then increased, step by step, and more supercharge applied until the same intensity of detonation was recorded; this process was continued until a point was reached at which no further enrichment was effective. In fact, after about 60% excess fuel, not only did further enrichment have no effect but there was even some indication that it increased the tendency to detonate. A finely pulverized water spray was then delivered into the induction pipe which served to suppress detonation, in part by the inter-cooling it provided, and in part by the influence of steam as an anti-detonant, and so allow of further supercharging. This was continued progressively, admitting just sufficient water at each stage to ward off detonation until a BMEP of 290 pounds per square inch was reached, which was found to be the limit of the dynamometer. At the same time, it was noted that, with the addition of water, the influence of steam as an anti-knock allowed the fuel/air ratio being much reduced. From this curve as shown in the figure above it will be seen that under these operating conditions a limiting BMEP that could be reached with 87 octane petrol alone at an economical mixture strength was 168 psi. By enriching the mixture to the limit of usefulness, the BMEP could be stepped up to 237 psi. By the introduction of water, it could be further stepped up 290 psi and probably more; at the same time the fuel/air ratio could be reduced once again; in fact with Gaseous IntercoolingT, no appreciable advantage was found from the use of an overrich fuel/air mixture. It will be noted that the total specific consumption of liquid, i.e., fuel plus water, is not so very much greater than when running on a very rich mixture of fuel alone."
"The slope of the curve of maximum cylinder pressure is interesting in that after the injection of water, it no longer rose but even tended very slightly to fall, and the same applied to the gross heat flow to the cooling water which reached a maximum at a BMEP of about 230 pounds per square inch, and thereafter fell off, until at a BMEP of 290 pounds per square inch it had fallen to the same level as that of 170 pounds without Gaseous IntercoolingT."
The result of this kind of test will vary with engine speed, engine size, compression ratio, fuel octane, etc. These variations are not important as far as the principle is concerned. The main thing the curve shows is detonation may be prevented up to a certain point by fuel enrichment, but after that point, water or water-alcohol injection must be used.
Water is usually combined with methanol (methyl-alcohol) in proportions up to 50-50 to increase the volatility of the injected mixture - and therefore its cooling effect - to add part fuel instead of all water for further horsepower increase, and to eliminate the possibility of the water freezing on a cold day. Harry Ricardo, again quoting from his book, The Higher Speed Internal combustion Engine, says "Higher percentages of methanol are not desirable because methanol, itself, is prone to pre-ignition."
http://www.carrollsupercharging.com/oldsite/index2.html
I found an interesting little tidbit..
We all have a tendency when we discover such phenomenon and the solution to it, to think we have "invented the wheel." This problem, for one, has been around a long time and Ricardo not only faced it but ran a series of tests in the early 1930's, plotted in the figure above, Reference: The High-Speed Internal Combustion Engine by H. Ricardo. To quote Mr. Ricardo, "In this case, running throughout at a speed of 2,500 RPM and with a compression ratio of 7:1, the engine was run on an economical mixture, i.e. about 10% weak, and supercharge applied to the first incidence of detonation, which occurred when the BMEP had reached 168 pounds per square inch. The mixture strength was then increased, step by step, and more supercharge applied until the same intensity of detonation was recorded; this process was continued until a point was reached at which no further enrichment was effective. In fact, after about 60% excess fuel, not only did further enrichment have no effect but there was even some indication that it increased the tendency to detonate. A finely pulverized water spray was then delivered into the induction pipe which served to suppress detonation, in part by the inter-cooling it provided, and in part by the influence of steam as an anti-detonant, and so allow of further supercharging. This was continued progressively, admitting just sufficient water at each stage to ward off detonation until a BMEP of 290 pounds per square inch was reached, which was found to be the limit of the dynamometer. At the same time, it was noted that, with the addition of water, the influence of steam as an anti-knock allowed the fuel/air ratio being much reduced. From this curve as shown in the figure above it will be seen that under these operating conditions a limiting BMEP that could be reached with 87 octane petrol alone at an economical mixture strength was 168 psi. By enriching the mixture to the limit of usefulness, the BMEP could be stepped up to 237 psi. By the introduction of water, it could be further stepped up 290 psi and probably more; at the same time the fuel/air ratio could be reduced once again; in fact with Gaseous IntercoolingT, no appreciable advantage was found from the use of an overrich fuel/air mixture. It will be noted that the total specific consumption of liquid, i.e., fuel plus water, is not so very much greater than when running on a very rich mixture of fuel alone."
"The slope of the curve of maximum cylinder pressure is interesting in that after the injection of water, it no longer rose but even tended very slightly to fall, and the same applied to the gross heat flow to the cooling water which reached a maximum at a BMEP of about 230 pounds per square inch, and thereafter fell off, until at a BMEP of 290 pounds per square inch it had fallen to the same level as that of 170 pounds without Gaseous IntercoolingT."
The result of this kind of test will vary with engine speed, engine size, compression ratio, fuel octane, etc. These variations are not important as far as the principle is concerned. The main thing the curve shows is detonation may be prevented up to a certain point by fuel enrichment, but after that point, water or water-alcohol injection must be used.
Water is usually combined with methanol (methyl-alcohol) in proportions up to 50-50 to increase the volatility of the injected mixture - and therefore its cooling effect - to add part fuel instead of all water for further horsepower increase, and to eliminate the possibility of the water freezing on a cold day. Harry Ricardo, again quoting from his book, The Higher Speed Internal combustion Engine, says "Higher percentages of methanol are not desirable because methanol, itself, is prone to pre-ignition."
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