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Increasing Induction Pressures

Increasing Induction Pressures December , 1932 AIRCRAFT ENGINEERIN G 315 Experiment s on the Effect on Power Output, Heat Losses and Fuel Consumption H E following extended summary of a th e ratio tends to decrease slightly as the wards the weak side as the induction pressure Report and Memorandum recently issued induction pressure is increased. is increased. By retarding the ignition, the by th e Aeronautical Research Committee* Fo r the Napier cylinder, using petrol, the mixture range is moved back towards its is printed here instead of in the ordinary pages above ratio (supercharger separately driven) position at normal induction pressure. devoted to Research Reports and Memoranda, increases slightly as the compression ratio is (4) Although the mixture strengths for where it would of necessity have to be very reduced, and decreases at each compression maximum power and maximum efficiency, considerably abbreviated, owing to the interest ratio as the induction pressure is raised, the alter in conformity with the movement of and importance of the work described. approximat e mean values being 1·53 a t 4·5 t o 1, th e complete range, the respective mixture The paper deals with experiments carried strengths giving maximum heat flow to the 1·58 at 4·0 to 1, and 1·63 at 3·5 to 1 com­ ou t in the Engineering Laboratory of the jackets and to exhaust remain unaltered pression ratio. University of Manchester on two different types under all conditions. Thermal Efficiency Constant of aero-engine cylinder. The cylinders were The alterations in the permissible mixture At a given compression ratio the indicated mounted on a R.A.E. Universal test bed, and range referred to above are more pronounced thermal efficiency remains approximately con­ supplied with compressed air from a separately in the results from the Rolls-Royce cylinder stan t at all induction pressures, provided that driven Reavell compressor, the air being passed under all conditions than in those from the th e ignition does not require to be retarded through an inter-cooler before being supplied Napier, in addition to which the available seriously, and that, at the lowest compression to the carburettor. mixture range is in all cases wider with the ratios, the induction pressure is sufficient to latter cylinder. Object of the Experiments ensure an adequate degree of turbulence. The object of th e experiments was to examine Subject to the above conditions, the ratio of Volumetric Efficiency Increase th e effects of increased induction pressure, at th e indicated thermal efficiency to the theo­ The volumetric efficiency, taken as the ratio a range of compression ratios, on the behaviour retical air cycle efficiency is constant at all (weight of air actually consumed) + (volume of the cylinders in regard to such variables as compression ratios, the value of the ratio being swept by the piston × density of air a t induc­ power output, heat losses and fuel consumption. approximately 0·617 for the Rolls-Royce cylin­ tio n temperature and pressure), increases con­ der at the 98 per cent full power mixture, The cylinders used for the tests were:—(1) A siderably as the induction pressure is raised, Napier E.77 type, two-valve, all-steel cylinder; using benzole as fuel. th e rate of increase becoming progressively less and (2) a Rolls-Royce F. type, four-valve With the mixture strength adjusted to give as the supercharge is increased. At a given cylinder, having a steel liner and aluminium 98 per cent full power and the supercharger induction pressure the rate of increase in alloy head. separately driven, the gain in brake thermal volumetric efficiency becomes less as the com­ A set of trials was first carried out, using the efficiency with increase in compression ratio is pression ratio is raised. Thus, whilst at normal Napier cylinder, at compression ratios of 4·5 to appreciably greater at normal induction pres­ induction pressure the volumetric efficiency is 1, 4·0 to 1, and 3·5 to 1. "Straight" Shell sures tha n is indicated by the expression giving approximately the same at all compression No . 1 petrol was used, the engine speed being th e standard air cycle efficiency. As the ratios, under supercharged conditions the 1,600 r.p.m. throughout. induction pressure is raised, the ratio (ob­ volumetric efficiency is reduced by an increase During each trial measurements were made served efficiency) + (air cycle efficiency) tends in compression ratio. t o increase more slowly with increase of com­ of the induction pressure, the power output, The rise in volumetric efficiency under super­ pression ratio, until, when conditions are such th e petrol and air consumption, and the heat charged conditions appears to be due to the flow t o cylinder jackets and to exhaust. With as to demand an appreciably retarded ignition fact that, under these conditions, not only has th e Napier cylinder, separate trials were run timing, the ratio reaches a maximum value th e swept volume to be filled with air, but in a t each compression ratio when the maximum and thereafter diminishes slightly. addition a further supply is required to fill up cylinder pressure was recorded at a range of th e clearance space, since a t the commencement compression ratios, using an Okill pressure Fuel Consumption of the charging stroke this space will contain indicator. At each compression ratio, with the super­ residuals at approximately atmospheric On completion of the above tests, the Rolls- charger separately driven, the fuel consumption pressure. Royce cylinder was mounted on the test bed per brake horse-power (at 9S per cent full At a given compression ratio, th e ratio (I.H.P.) and a second set of trials was carried out at an power) decreases as the induction pressure is + (weight of charge per minute) is constant and engine speed of 1,600 r.p.m. Except for one increased, the rate of decrease being greatest independent of the induction pressure, pro­ series of trials with petrol at 4·0 to 1 com­ a t the commencement of the range and be­ vided conditions are not such as to require a pression ratio, the fuel used with the Rolls- coming less as the supercharge is increased. seriously retarded ignition timing. The value of Royce cylinder was in all cases pure benzole. A t a given induction pressure the rate of th e ratio is moreover the same for both cylinders With this fuel a series of trials was carried out at decrease becomes less as the compression ratio a t the same compression ratio, and remains each of the following compression ratios, vis., is raised. At each compression ratio a point unchanged whether the fuel is petrol or benzole. 4·0, 5·0, 5·5, 6·0, 6·5, and 7·0 to 1. is reached when further increase of induction With constant induction temperature the pressure no longer gives a decrease in specific I.M.E.P. increases at a constant rate as the The Results Summarized consumption, this point coinciding with the induction pressure is increased. For the Rolls- The results indicate that:— poin t at which conditions become such as to Royce cylinder, at the maximum power mixture (1) At all compression ratios the per­ demand an appreciably retarded ignition timing. strength, the value of the ratio (percentage missible mixture range is narrowed by in­ At the point referred to, for the Rolls-Royce increase in I.M.E.P.) + (percentage increase in crease of induction pressure. cylinder, the decrease in specific consumption, absolute induction pressure) is approximately (2) As the compression ratio is raised, at expressed as a percentage of th e value a t normal 1·555 at all compression ratios. an y given induction pressure, the working induction pressure, is approximately 26 per Fo r the Rolls-Royce cylinder, irrespective of mixture range is extended. cent at 4·0 to 1, 16 per cent at 5·0 to 1, 9 per compression ratio, the mean value of the (3) If the ignition timing remains un­ cent at 6·0 to 1, and 5 per cent at 7·0 t o 1 com­ ratio (percentage increase in B.M.E.P.) + altered, the complete range of permissible pression ratio. When allowance is made for the (percentage increase in absolute induction mixture strengths moves progressively to­ supercharger being driven by the engine (at pressure), a t maximum power mixture strength, 65 per cent adiabatic efficiency), the above is approximately 1·49 with the supercharger percentages become approximately 16 per cent * R. & M. No. 1460. November, 1931. separately driven, and approximately 1·27 a t 4·0 to 1, 8 per cent a t 5·0 to 1, 4·0 per cent at Experiments with a Supercharged Single- when allowance is made for the supercharger 6·0 t o 1, and 1 per cent at 7·0 to 1 compression Cylinder Unit. By G. F . Mucklow. being driven from the engine at 65 per cent ratio . (H. M. Stationery Office, 3s.) adiabatic efficiency, though in the latter case http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Aircraft Engineering and Aerospace Technology Emerald Publishing

Increasing Induction Pressures

Aircraft Engineering and Aerospace Technology , Volume 4 (12): 1 – Dec 1, 1932

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Emerald Publishing
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Copyright © Emerald Group Publishing Limited
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0002-2667
DOI
10.1108/eb029633
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Abstract

December , 1932 AIRCRAFT ENGINEERIN G 315 Experiment s on the Effect on Power Output, Heat Losses and Fuel Consumption H E following extended summary of a th e ratio tends to decrease slightly as the wards the weak side as the induction pressure Report and Memorandum recently issued induction pressure is increased. is increased. By retarding the ignition, the by th e Aeronautical Research Committee* Fo r the Napier cylinder, using petrol, the mixture range is moved back towards its is printed here instead of in the ordinary pages above ratio (supercharger separately driven) position at normal induction pressure. devoted to Research Reports and Memoranda, increases slightly as the compression ratio is (4) Although the mixture strengths for where it would of necessity have to be very reduced, and decreases at each compression maximum power and maximum efficiency, considerably abbreviated, owing to the interest ratio as the induction pressure is raised, the alter in conformity with the movement of and importance of the work described. approximat e mean values being 1·53 a t 4·5 t o 1, th e complete range, the respective mixture The paper deals with experiments carried strengths giving maximum heat flow to the 1·58 at 4·0 to 1, and 1·63 at 3·5 to 1 com­ ou t in the Engineering Laboratory of the jackets and to exhaust remain unaltered pression ratio. University of Manchester on two different types under all conditions. Thermal Efficiency Constant of aero-engine cylinder. The cylinders were The alterations in the permissible mixture At a given compression ratio the indicated mounted on a R.A.E. Universal test bed, and range referred to above are more pronounced thermal efficiency remains approximately con­ supplied with compressed air from a separately in the results from the Rolls-Royce cylinder stan t at all induction pressures, provided that driven Reavell compressor, the air being passed under all conditions than in those from the th e ignition does not require to be retarded through an inter-cooler before being supplied Napier, in addition to which the available seriously, and that, at the lowest compression to the carburettor. mixture range is in all cases wider with the ratios, the induction pressure is sufficient to latter cylinder. Object of the Experiments ensure an adequate degree of turbulence. The object of th e experiments was to examine Subject to the above conditions, the ratio of Volumetric Efficiency Increase th e effects of increased induction pressure, at th e indicated thermal efficiency to the theo­ The volumetric efficiency, taken as the ratio a range of compression ratios, on the behaviour retical air cycle efficiency is constant at all (weight of air actually consumed) + (volume of the cylinders in regard to such variables as compression ratios, the value of the ratio being swept by the piston × density of air a t induc­ power output, heat losses and fuel consumption. approximately 0·617 for the Rolls-Royce cylin­ tio n temperature and pressure), increases con­ der at the 98 per cent full power mixture, The cylinders used for the tests were:—(1) A siderably as the induction pressure is raised, Napier E.77 type, two-valve, all-steel cylinder; using benzole as fuel. th e rate of increase becoming progressively less and (2) a Rolls-Royce F. type, four-valve With the mixture strength adjusted to give as the supercharge is increased. At a given cylinder, having a steel liner and aluminium 98 per cent full power and the supercharger induction pressure the rate of increase in alloy head. separately driven, the gain in brake thermal volumetric efficiency becomes less as the com­ A set of trials was first carried out, using the efficiency with increase in compression ratio is pression ratio is raised. Thus, whilst at normal Napier cylinder, at compression ratios of 4·5 to appreciably greater at normal induction pres­ induction pressure the volumetric efficiency is 1, 4·0 to 1, and 3·5 to 1. "Straight" Shell sures tha n is indicated by the expression giving approximately the same at all compression No . 1 petrol was used, the engine speed being th e standard air cycle efficiency. As the ratios, under supercharged conditions the 1,600 r.p.m. throughout. induction pressure is raised, the ratio (ob­ volumetric efficiency is reduced by an increase During each trial measurements were made served efficiency) + (air cycle efficiency) tends in compression ratio. t o increase more slowly with increase of com­ of the induction pressure, the power output, The rise in volumetric efficiency under super­ pression ratio, until, when conditions are such th e petrol and air consumption, and the heat charged conditions appears to be due to the flow t o cylinder jackets and to exhaust. With as to demand an appreciably retarded ignition fact that, under these conditions, not only has th e Napier cylinder, separate trials were run timing, the ratio reaches a maximum value th e swept volume to be filled with air, but in a t each compression ratio when the maximum and thereafter diminishes slightly. addition a further supply is required to fill up cylinder pressure was recorded at a range of th e clearance space, since a t the commencement compression ratios, using an Okill pressure Fuel Consumption of the charging stroke this space will contain indicator. At each compression ratio, with the super­ residuals at approximately atmospheric On completion of the above tests, the Rolls- charger separately driven, the fuel consumption pressure. Royce cylinder was mounted on the test bed per brake horse-power (at 9S per cent full At a given compression ratio, th e ratio (I.H.P.) and a second set of trials was carried out at an power) decreases as the induction pressure is + (weight of charge per minute) is constant and engine speed of 1,600 r.p.m. Except for one increased, the rate of decrease being greatest independent of the induction pressure, pro­ series of trials with petrol at 4·0 to 1 com­ a t the commencement of the range and be­ vided conditions are not such as to require a pression ratio, the fuel used with the Rolls- coming less as the supercharge is increased. seriously retarded ignition timing. The value of Royce cylinder was in all cases pure benzole. A t a given induction pressure the rate of th e ratio is moreover the same for both cylinders With this fuel a series of trials was carried out at decrease becomes less as the compression ratio a t the same compression ratio, and remains each of the following compression ratios, vis., is raised. At each compression ratio a point unchanged whether the fuel is petrol or benzole. 4·0, 5·0, 5·5, 6·0, 6·5, and 7·0 to 1. is reached when further increase of induction With constant induction temperature the pressure no longer gives a decrease in specific I.M.E.P. increases at a constant rate as the The Results Summarized consumption, this point coinciding with the induction pressure is increased. For the Rolls- The results indicate that:— poin t at which conditions become such as to Royce cylinder, at the maximum power mixture (1) At all compression ratios the per­ demand an appreciably retarded ignition timing. strength, the value of the ratio (percentage missible mixture range is narrowed by in­ At the point referred to, for the Rolls-Royce increase in I.M.E.P.) + (percentage increase in crease of induction pressure. cylinder, the decrease in specific consumption, absolute induction pressure) is approximately (2) As the compression ratio is raised, at expressed as a percentage of th e value a t normal 1·555 at all compression ratios. an y given induction pressure, the working induction pressure, is approximately 26 per Fo r the Rolls-Royce cylinder, irrespective of mixture range is extended. cent at 4·0 to 1, 16 per cent at 5·0 to 1, 9 per compression ratio, the mean value of the (3) If the ignition timing remains un­ cent at 6·0 to 1, and 5 per cent at 7·0 t o 1 com­ ratio (percentage increase in B.M.E.P.) + altered, the complete range of permissible pression ratio. When allowance is made for the (percentage increase in absolute induction mixture strengths moves progressively to­ supercharger being driven by the engine (at pressure), a t maximum power mixture strength, 65 per cent adiabatic efficiency), the above is approximately 1·49 with the supercharger percentages become approximately 16 per cent * R. & M. No. 1460. November, 1931. separately driven, and approximately 1·27 a t 4·0 to 1, 8 per cent a t 5·0 to 1, 4·0 per cent at Experiments with a Supercharged Single- when allowance is made for the supercharger 6·0 t o 1, and 1 per cent at 7·0 to 1 compression Cylinder Unit. By G. F . Mucklow. being driven from the engine at 65 per cent ratio . (H. M. Stationery Office, 3s.) adiabatic efficiency, though in the latter case

Journal

Aircraft Engineering and Aerospace TechnologyEmerald Publishing

Published: Dec 1, 1932

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