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Hydrogen-powered lawn mower
0360-3199/93 $6.00 + 0.00 Pergamon Press Ltd. © 1993 International Associationfor Hydrogen Energy.
Int. J. HydrogenEnergy,Vol. 18, No. 4, pp. 345-348, 1993. Printed in Great Britain.
HYDROGEN-POWERED LAWN MOWER K. YVON and J.-L. LORENZONI Laboratoire de Cristallographie, Universit6 de Gen~ve, 24, quai Ernest Ansermet, CH-121 i Gen~ve 4, Switzerland
(Received for publication 13 October 1992) Abstract--We present a hydrogen-powered lawn mower which was adapted from a commercial model running on gasoline. The necessary modifications include adjustments to the carburettor and the installation of a hydrogen reservoir containing about 5 kg of a metal hydride powder. Hydrogen is obtained by desorption of that powder at ambient temperature and 2 - 2 0 bar pressure. The reservoir is rechargable at a hydrogen pressure of about 25 bar within less than 1 h. One charge lasts about 40 min, corresponding to about 800 m 2 of cut lawn. The engine shows a reduced noise level and no tendency to backfiring. The prototype has run successfully for more than 1 year.
INTRODUCTION Applications of metal hydrides for internal combustion (I.C.) engines have been known for some time (for reviews see Refs I-l] and [2]). Most concern the automobile sector (see for example Ref. [3]). Car engines usually run at relatively high rpm and have to sustain relatively rapid changes in rpm. Thus, they require rather important modifications to their carburettors if operated on hydrogen in order to prevent backfiring [4]. Moreover, the weight and price of the metal hydride reservoirs actually available are considered to be serious drawbacks for these type of applications. For those reasons, small I.C. engines are generally considered to be less attractive for hydrogen operation and metal hydride applications. In this communication we show that this view is not necessarily correct. Lawn mower engines, for example, run at relatively low and constant rpm and thus are not expected to require major changes to their carburettor systems if adapted to run on hydrogen. They also do not need a large fuel supply, and thus are not expected to be much handicapped by the weight increase due to the installation of a small metal hydride storage tank. In order to demonstrate the feasibility of such a small-scale application, we have adapted a commercially available gasoline powered model to run on hydrogen stored as a metal hydride. In this paper, we describe the necessary modifications, and report on the technical specifications and performance of the prototype. EXPERIMENTAL A small, commercially sold, hand-operated, gasolinepowered four-stroke engine model was acquired (for technical specifications see Table 1). The modifications necessary for operation on hydrogen concerned mainly the carburettor and the fuel tank. Carburettor. The engine was equipped with a conventional carburettor (Fig. 1) which was changed as follows.
The carburettor float (7) and principal jet (5) were removed and replaced by a hydrogen injector nozzle (5') made of brass which had an inner diameter of 1.6 mm, an outer diameter of 6 mm and a length of 43.9 mm. The injector nozzle was introduced through the carburettor housing (6), placed in a coaxial position and connected via a needle valve to a metal hydride storage tank (see below). These changes are described in more detail elsewhere [5]. Metal hydride storage tank. For convenience, a commercially available model [6] was chosen. It consists of a stainless steel cylinder which contains 5 kg of a metal hydride powder and is surrounded by aluminium ribs in order to favor heat transfer during absorption and desorption. Its total weight is 12 kg, and it allows the storage of a volume of about ! m 3 of hydrogen gas at ambient conditions. The pressure of the hydrogen gas released is 3 - 2 5 bar and depends on the temperature and state of discharge of the storage tank. The cylinder was fixed above the engine on the metal tubes of the handles of the lawn mower. The hydrogen content was monitored by a pressure gauge mounted on the reservoir. During desorption, the reservoir cooled by up to 15°C. Operation and performance. The modified lawn mower is represented in Fig. 2. The engine speed was regulated by the needle valve (2) which controlled the hydrogen supply, and the carburettor choke (4) which controlled the air supply. The maximum speed obtained was comparable to that of the gasoline powered model (2000-3000 rpm), whereas the maximum power was lower by a factor of about 20~o. Interestingly, the noise level was significantly reduced (70 dB, instead of 72 dB for the gasoline powered model, as measured at 5 m distance and at 2500 rpm) and no tendency to backfiring was observed (presumably because of the low and constant engine speed). On one charge of hydrogen the lawn mower ran for typically 3 0 - 4 0 rain, corresponding to approximately 800 m 2 of cut lawn. The exhaust gases were found to consist mainly
345
346
K. YVON and J.-L. LORENZONI Table 1. Technical specifications Motor
HONDA, model HR 173, four-stroke, one cylinder (capacity: 80 cm3), electronic ignition (spark-plug), regulation by needle valve (SWAGELOCK) for hydrogen supply and carburettor choke for air supply
Carburettor
Gasoline model (Fig. 1), adapted as described in the text
Reservoir
Commercially available [6] metal hydride tank, model KL 114-1, containing 5 kg of a hydrogenated alloy (code 5800) of titanium, vanadium, manganese, chromium, zirconium and iron; total weight of reservoir: 12 kg; volume of stored hydrogen: 1 m 3 at ambient conditions; pressure of hydrogen desorbed at ambient temperature; 3-25 bar
Recharge
From a commercially available pressurized hydrogen gas cylinder (volume: 50 1; pressure: 200 bar) allowing approximately 10 recharges; duration of recharge: less than 1 h, depending on the temperature of the reservoir, which warms by approximately 30°C during recharge; hydrogen pressure required for recharge: 25 bar; number of possible recharges: more than 1000 (depending on the purity of the hydrogen used)
Performance
Speed:comparable to the gasoline powered model (2000-3000 rpm). Power: about 20~o less than the gasoline powered model running at the same rpm. Operation time per charge: 30-40 rain, corresponding to about 800 m 2 of cut lawn. Exhaust gases: Water vapor, small quantities of nitric oxide (0.3 ppm) and nitrogen dioxide (1.6 ppm). Noise level: lower than that of the gasoline powered model (70 dB instead of 72 dB, as measured at 5 m distance and 2500 rpm)
Operating costs
Approximately 7 SFr/recharge, corresponding to about 1 m 3 of hydrogen gas of 99.95% purity at normal conditions
Operating periods
Summer 1991 and summer 1992
of water vapor, nitrogen and minor amounts of nitrogen oxides. Recharging. As the hydrogen pressure in the storage tank dropped below 3 bar, the reservoir was disconnected from the engine and recharged at 25 bar pressure by connecting its outlet to a pressurized hydrogen gas cylinder (commercially available model, volume 50 I, hydrogen pressure 200 bar, 99.9997% purity). One cylinder made about 10 recharges, which was sufficient for the operation of the lawn mower for one season. The necessary time for a complete recharge varied typically between 20 and 60 min and depended on the temperature of the storage tank. Since that temperature increased during absorption by about 30°C, shorter charging times required immersion of the storage tank in cold water. Up to now (September 1992) twenty recharges were made, corresponding to a total operation time of the engine of about 14 h. No degradation of the sorption properties of the storage tank has been observed. The number of possible recharges is presumably higher than 1000 and depends on the purity of the hydrogen used. Relevant technical specifications are summarized in Table 1. Servicing. The engine has not been serviced. After one year of operation, the lubricating oil was practically colorless and showed no sign of degradation.
CONCLUSIONS The performance and successful operation of the lawn mower shows that small I.C. engines can be more easily adapted to run on hydrogen than large I.C. engines, and that metal hydrides are technically feasible storage media for some applications of these engines. As with other applications of this type, their main interest comes from the ecological advantage of hydrogen: it is a non-polluting, non-toxic, odorless and colorless fuel; its only combustion products are water and, if burned in air, small quantities of nitrogen oxides; contrary to fossil fuels, it is a renewable energy source: it is compact and safe (non-explosive) when stored in solid form as metal hydrides; and finally, hydrogen powered I.C. engines appear to run more quietly than their gasoline counterparts. All these advantages can be appreciated in ecologically (or socially) sensitive environments such as gardens, parks, golf courses, graveyards, etc. Thus, applications like the one presented here appear to be well-suited to inform a greater public about the state of the art in hydrogen technology and metal hydride applications, and about safety aspects which are often incorrectly assessed. As to the shortcomings of hydrogen and metal hydrides, some, such as the loss of power of I.C. engines and the relatively high
347
H Y D R O G E N - P O W E R E D LAWN MOWER
before
after 1
2 3
7
5
Fig. 1. Carburettor before and after modifications: (1) idling jet; (2) carburettor choke tube; (3) air inlet; (4) float chamber; (5) principal fuel jet; (5') hydrogen injector nozzle; (6) carburettor chamber; (7) float.
348
K. YVON and J.-L. LORENZONI
4 3
Fig. 2. Prototype of hydrogen powered lawn mower: (1) metal hydride storage tank: (2) regulation valve; (3) pressure gauge; (4) choke level; (5) carburettor choke.
costs of operation, do not constitute major drawbacks. Other drawbacks, such as the relatively high weight and costs of the hydrogen storage elements and the poor hydrogen distribution system, are more serious. Future research should therefore concentrate on reducing the weight and costs of the hydrogen storage elements, and an effort should be made by public utilities to develop a more efficient hydrogen distribution system.
Acknowledgements--The authors thank W. Kloeti and the Service de l'Ecotoxicologue Cantonal for the analysis of the engine exhaust gases. This work was supported by the Swiss Federal Office of Energy in the frame of the Swiss Hydrogen Energy Research Programme.
REFERENCES 1. G. Sandrock, S. Suda and L. Schlapbach, in L. Schlapbach (Ed.) Hydrogen in lntermetaUic Compounds H, Topics in Applied Physics, Vol. 67, Chap. 5. Springer, Berlin (1992). 2. O. Bernauer, Z. Phys. Chem., N.F. 164, 1381 (1989). 3. J. TOpler and K. Feucht, Z. Phys. Chem., N.F. 164, 1451 (1989). 4. L. M. Das, Int. J. Hydrogen Energy 15, 833; 425 (1990). 5. Swiss Patent Application no. 830-92-7 (1992). 6. HWT Gesellschaft fiir Hydrid und Wasserstofftechnik m.b.H. Miilheim a.d.R., Germany.
Int. J. HydrogenEnergy,Vol. 18, No. 4, pp. 345-348, 1993. Printed in Great Britain.
HYDROGEN-POWERED LAWN MOWER K. YVON and J.-L. LORENZONI Laboratoire de Cristallographie, Universit6 de Gen~ve, 24, quai Ernest Ansermet, CH-121 i Gen~ve 4, Switzerland
(Received for publication 13 October 1992) Abstract--We present a hydrogen-powered lawn mower which was adapted from a commercial model running on gasoline. The necessary modifications include adjustments to the carburettor and the installation of a hydrogen reservoir containing about 5 kg of a metal hydride powder. Hydrogen is obtained by desorption of that powder at ambient temperature and 2 - 2 0 bar pressure. The reservoir is rechargable at a hydrogen pressure of about 25 bar within less than 1 h. One charge lasts about 40 min, corresponding to about 800 m 2 of cut lawn. The engine shows a reduced noise level and no tendency to backfiring. The prototype has run successfully for more than 1 year.
INTRODUCTION Applications of metal hydrides for internal combustion (I.C.) engines have been known for some time (for reviews see Refs I-l] and [2]). Most concern the automobile sector (see for example Ref. [3]). Car engines usually run at relatively high rpm and have to sustain relatively rapid changes in rpm. Thus, they require rather important modifications to their carburettors if operated on hydrogen in order to prevent backfiring [4]. Moreover, the weight and price of the metal hydride reservoirs actually available are considered to be serious drawbacks for these type of applications. For those reasons, small I.C. engines are generally considered to be less attractive for hydrogen operation and metal hydride applications. In this communication we show that this view is not necessarily correct. Lawn mower engines, for example, run at relatively low and constant rpm and thus are not expected to require major changes to their carburettor systems if adapted to run on hydrogen. They also do not need a large fuel supply, and thus are not expected to be much handicapped by the weight increase due to the installation of a small metal hydride storage tank. In order to demonstrate the feasibility of such a small-scale application, we have adapted a commercially available gasoline powered model to run on hydrogen stored as a metal hydride. In this paper, we describe the necessary modifications, and report on the technical specifications and performance of the prototype. EXPERIMENTAL A small, commercially sold, hand-operated, gasolinepowered four-stroke engine model was acquired (for technical specifications see Table 1). The modifications necessary for operation on hydrogen concerned mainly the carburettor and the fuel tank. Carburettor. The engine was equipped with a conventional carburettor (Fig. 1) which was changed as follows.
The carburettor float (7) and principal jet (5) were removed and replaced by a hydrogen injector nozzle (5') made of brass which had an inner diameter of 1.6 mm, an outer diameter of 6 mm and a length of 43.9 mm. The injector nozzle was introduced through the carburettor housing (6), placed in a coaxial position and connected via a needle valve to a metal hydride storage tank (see below). These changes are described in more detail elsewhere [5]. Metal hydride storage tank. For convenience, a commercially available model [6] was chosen. It consists of a stainless steel cylinder which contains 5 kg of a metal hydride powder and is surrounded by aluminium ribs in order to favor heat transfer during absorption and desorption. Its total weight is 12 kg, and it allows the storage of a volume of about ! m 3 of hydrogen gas at ambient conditions. The pressure of the hydrogen gas released is 3 - 2 5 bar and depends on the temperature and state of discharge of the storage tank. The cylinder was fixed above the engine on the metal tubes of the handles of the lawn mower. The hydrogen content was monitored by a pressure gauge mounted on the reservoir. During desorption, the reservoir cooled by up to 15°C. Operation and performance. The modified lawn mower is represented in Fig. 2. The engine speed was regulated by the needle valve (2) which controlled the hydrogen supply, and the carburettor choke (4) which controlled the air supply. The maximum speed obtained was comparable to that of the gasoline powered model (2000-3000 rpm), whereas the maximum power was lower by a factor of about 20~o. Interestingly, the noise level was significantly reduced (70 dB, instead of 72 dB for the gasoline powered model, as measured at 5 m distance and at 2500 rpm) and no tendency to backfiring was observed (presumably because of the low and constant engine speed). On one charge of hydrogen the lawn mower ran for typically 3 0 - 4 0 rain, corresponding to approximately 800 m 2 of cut lawn. The exhaust gases were found to consist mainly
345
346
K. YVON and J.-L. LORENZONI Table 1. Technical specifications Motor
HONDA, model HR 173, four-stroke, one cylinder (capacity: 80 cm3), electronic ignition (spark-plug), regulation by needle valve (SWAGELOCK) for hydrogen supply and carburettor choke for air supply
Carburettor
Gasoline model (Fig. 1), adapted as described in the text
Reservoir
Commercially available [6] metal hydride tank, model KL 114-1, containing 5 kg of a hydrogenated alloy (code 5800) of titanium, vanadium, manganese, chromium, zirconium and iron; total weight of reservoir: 12 kg; volume of stored hydrogen: 1 m 3 at ambient conditions; pressure of hydrogen desorbed at ambient temperature; 3-25 bar
Recharge
From a commercially available pressurized hydrogen gas cylinder (volume: 50 1; pressure: 200 bar) allowing approximately 10 recharges; duration of recharge: less than 1 h, depending on the temperature of the reservoir, which warms by approximately 30°C during recharge; hydrogen pressure required for recharge: 25 bar; number of possible recharges: more than 1000 (depending on the purity of the hydrogen used)
Performance
Speed:comparable to the gasoline powered model (2000-3000 rpm). Power: about 20~o less than the gasoline powered model running at the same rpm. Operation time per charge: 30-40 rain, corresponding to about 800 m 2 of cut lawn. Exhaust gases: Water vapor, small quantities of nitric oxide (0.3 ppm) and nitrogen dioxide (1.6 ppm). Noise level: lower than that of the gasoline powered model (70 dB instead of 72 dB, as measured at 5 m distance and 2500 rpm)
Operating costs
Approximately 7 SFr/recharge, corresponding to about 1 m 3 of hydrogen gas of 99.95% purity at normal conditions
Operating periods
Summer 1991 and summer 1992
of water vapor, nitrogen and minor amounts of nitrogen oxides. Recharging. As the hydrogen pressure in the storage tank dropped below 3 bar, the reservoir was disconnected from the engine and recharged at 25 bar pressure by connecting its outlet to a pressurized hydrogen gas cylinder (commercially available model, volume 50 I, hydrogen pressure 200 bar, 99.9997% purity). One cylinder made about 10 recharges, which was sufficient for the operation of the lawn mower for one season. The necessary time for a complete recharge varied typically between 20 and 60 min and depended on the temperature of the storage tank. Since that temperature increased during absorption by about 30°C, shorter charging times required immersion of the storage tank in cold water. Up to now (September 1992) twenty recharges were made, corresponding to a total operation time of the engine of about 14 h. No degradation of the sorption properties of the storage tank has been observed. The number of possible recharges is presumably higher than 1000 and depends on the purity of the hydrogen used. Relevant technical specifications are summarized in Table 1. Servicing. The engine has not been serviced. After one year of operation, the lubricating oil was practically colorless and showed no sign of degradation.
CONCLUSIONS The performance and successful operation of the lawn mower shows that small I.C. engines can be more easily adapted to run on hydrogen than large I.C. engines, and that metal hydrides are technically feasible storage media for some applications of these engines. As with other applications of this type, their main interest comes from the ecological advantage of hydrogen: it is a non-polluting, non-toxic, odorless and colorless fuel; its only combustion products are water and, if burned in air, small quantities of nitrogen oxides; contrary to fossil fuels, it is a renewable energy source: it is compact and safe (non-explosive) when stored in solid form as metal hydrides; and finally, hydrogen powered I.C. engines appear to run more quietly than their gasoline counterparts. All these advantages can be appreciated in ecologically (or socially) sensitive environments such as gardens, parks, golf courses, graveyards, etc. Thus, applications like the one presented here appear to be well-suited to inform a greater public about the state of the art in hydrogen technology and metal hydride applications, and about safety aspects which are often incorrectly assessed. As to the shortcomings of hydrogen and metal hydrides, some, such as the loss of power of I.C. engines and the relatively high
347
H Y D R O G E N - P O W E R E D LAWN MOWER
before
after 1
2 3
7
5
Fig. 1. Carburettor before and after modifications: (1) idling jet; (2) carburettor choke tube; (3) air inlet; (4) float chamber; (5) principal fuel jet; (5') hydrogen injector nozzle; (6) carburettor chamber; (7) float.
348
K. YVON and J.-L. LORENZONI
4 3
Fig. 2. Prototype of hydrogen powered lawn mower: (1) metal hydride storage tank: (2) regulation valve; (3) pressure gauge; (4) choke level; (5) carburettor choke.
costs of operation, do not constitute major drawbacks. Other drawbacks, such as the relatively high weight and costs of the hydrogen storage elements and the poor hydrogen distribution system, are more serious. Future research should therefore concentrate on reducing the weight and costs of the hydrogen storage elements, and an effort should be made by public utilities to develop a more efficient hydrogen distribution system.
Acknowledgements--The authors thank W. Kloeti and the Service de l'Ecotoxicologue Cantonal for the analysis of the engine exhaust gases. This work was supported by the Swiss Federal Office of Energy in the frame of the Swiss Hydrogen Energy Research Programme.
REFERENCES 1. G. Sandrock, S. Suda and L. Schlapbach, in L. Schlapbach (Ed.) Hydrogen in lntermetaUic Compounds H, Topics in Applied Physics, Vol. 67, Chap. 5. Springer, Berlin (1992). 2. O. Bernauer, Z. Phys. Chem., N.F. 164, 1381 (1989). 3. J. TOpler and K. Feucht, Z. Phys. Chem., N.F. 164, 1451 (1989). 4. L. M. Das, Int. J. Hydrogen Energy 15, 833; 425 (1990). 5. Swiss Patent Application no. 830-92-7 (1992). 6. HWT Gesellschaft fiir Hydrid und Wasserstofftechnik m.b.H. Miilheim a.d.R., Germany.