Test of blends of hydrogen and natural gas in a light duty vehicle

Transcription

1 JSAE 277XXX SAE 27-1-YYYY Test of blends of hydrogen and natural gas in a light duty vehicle Giovanni Pede, Ennio Rossi Italian National Agency for New Technologies, Energy and the Environment (ENEA) Department of Energy Technologies Maria Chiesa Catholic University of Brescia (Italy) Environmental Physics Department Fernando Ortenzi DITS Dipartimento di Idraulica Trasporti e Strade, University La Sapienza,Rome (Italy) Copyright 27 Society of Automotive Engineers of Japan, Inc. and Copyright 27 SAE International ABSTRACT Hydrogen-enriched combustion has been studied by several institutions and companies over the last three decades. The purpose of adding hydrogen to conventional fuels is to extend the lean limit of combustion because hydrogen improves flame stability and allows a lower temperature combustion. Even with stoichiometric mixture, HCNG advantages had been demonstrated, since blends determine a reduction of noxious emissions. In the framework of an EU project called BONG-HY, bench tests with HCNG on a natural gas vehicle had been carried on at ENEA. Results of lab tests show a fair improvement of the efficiency and CO2 emissions as well as an overall improvement regarding local pollutants. INTRODUCTION The growing sector of transports rises a big alarm either for the day-by-day increasing number of vehicles and for the sensible contribution to the degradation of air quality in urban areas, as well as for the global pollution. In Italy, with beyond 35 million of circulating vehicles, the consumption of primary energy, all coming from fossil sources, accounts for more than 3%, which roughly leads to a corresponding 3% increase in CO 2 emissions. The European Union committed to the goal of reducing its dependence on imported fossil fuels (oil, natural gas, coal), by using at least 2% of alternative fuels within the year 22; the corresponding commitment in the reduction of Greenhouse Gases (GHG) is the well-known 8% with respect to 199 by 212, as required by the Kyoto Protocol. In Europe the sector of transports is responsible for the 25% of CO 2 emissions, 4% of which is related to the vehicles circulating in urban areas. External costs due to the degradation of air quality related to transports had been estimated in about 11.7% of EU GDP, corresponding to an outstanding value of 36 /year per citizen. Those alarming data have to be added to the contribution to the total emissions from the energetic sector (carbon dioxide, natural gas, nitrogen oxides, sulphur, aromatic compounds,.), which amounts at about 5% of the total contribution. Deaths caused by the smog, due to particulates and other emissions, are about 8 per year just for Italy; on the other side, the global change becomes a real problem, with an increasing concern about GHG emissions. Nowadays a last-generation Euro4 car emits slightly less than 15 grco 2 /km, with scarce perspectives to be able to reduce, with fossil fuels, that value very much. It had been worldwide agreed that the introduction of hydrogen as a new fuel could have contributed to the realization of a sustainable energy system in the long term (25 and beyond); according to this vision, emissions of both global and local pollutants can be maintained under safe values. Even if the transition towards a hydrogen-based economy will be surely very long, its sustainability is achievable since now, also considering the limitations in the substitution of conventional fuels with alternative ones, less polluting. Also the contribution of the introduction of biomass-derived

2 fuels, for a limited quota of total consumption, is counterbalanced by the still growing demand of vehicles in the world ( see Fig. 1 at the end) [1]. Even if it s difficult to forecast the future concerning the next decades, it has been agreed worldwide that climate change is closely connected with GHG emissions, so we may ask for some important decisions for the beyond-kyoto years. The stabilization of CO 2 concentration at values not higher than 55 ppm (today s value is 38 ppm) requires a strong emissions reduction: some of the IPCC scenarios aiming at that values shows a required decrease of GHG of 4-6% with respect to 199, which means a real reduction of 7-9% of the emissions with respect to the business-asusual forecast. Such a reduction won t ever be achieved by using any actual available sustainable technology. Nevertheless, a cultural shift will be necessary, in order to reach that goal: the introduction of hydrogen as an energy carrier seems to be a real contribution to that goal, making possible, in the long term, the realization of a cleaner World. METHANE-HYDROGEN MIXTURES A good opportunity in the short term can be represented by the utilization of blends of hydrogen with other fuels, first of all with natural gas (HCNG). When used in an Internal Combustion Engine (ICE), even the addition of a small amount of hydrogen to natural gas (5-3% by volume, that means ~1.5-1% by energy) leads to many advantages, because of some particular physical and chemical properties of the two fuels. HCNG15 Because of the characteristics of hydrogen, HCNG, despite its higher LHV per kg, has a lower LHV per Nm 3, depending on the hydrogen content. Therefore, a natural gas engine, when fuelled with HCNG, shows a lower power output, while maintaining its better efficiency. LHV LHV (MJ/kg) LHV (MJ/m3) % volume H2 Fig.3 In case of turbocharged engines, power output can be increased again by a simple increase of the charging pressure, possible even because of the higher reluctance to detonation of hydrogen. Additionally, CO2 emissions had been reduced not only as a result of the substitution of CNG by hydrogen. The special properties of hydrogen as a combustion stimulant can produce leverage factors much greater than 1 by improving fossil fuels--not just displacing them. Hydrogen leverage is defined as the following ratio : (% Emissions Reduction)/(% Energy Supplied as Hydrogen). The increased efficiency makes this value higher than 1. An obvious benefit of the leverage effect is that a CO 2 reduction is possible even if needed hydrogen is produced by natural gas without any sequestration of CO 2. STATE OF THE ART lambda=1 CH4 First experiences of methane-hydrogen mixture, with vehicles, were carried on in the framework of a programme financed by DOE and NREL, in Colorado, the "Denver Hythane Project, from 1991 to 1993, whose results are shown in the table below: Table 1 Denver Hythane Project Fig.2 Methane has a slow flame speed while hydrogen has a flame speed about eight times higher; when the air/fuel ratio (lambda) is much higher than for the stoichiometric condition the combustion of methane is not as stable as with HCNG. As a consequence of the addition of hydrogen to natural gas an overall better combustion had been verified, even in a wide range of operating conditions (lambda, compression ratio, etc.), finding the following main benefits: a higher efficiency lower emissions NMHC (g/mile) CO (g/mile) NOx (g/mile) Gasoline ULEV Natural gas Hythane In a next phase, according to an exhaustive review by R. Sierens and E. Rosseel, by University of Gent, Belgium that relates to laboratory testings in the second half of 9, many other experiences are recorded:

3 «Hoekstra et al. (1994, 1995) examined a V8 Chevrolet 35 engine at one particular speed (12.7 kw, 17 rpm) with different hydrogen enriched compressed natural gas mixtures, to simulate a light-duty truck. They found extremely low NOx values at λ =1.6 (φ =.625) for the 28 and 36 percent H2 blends Swain et al. (1993) and Yusuf et al. (1997) made tests with a 2 percent hydrogen 8 percent natural gas blend on two engines (2L Nissan and 1.6L Toyota) under light load conditions...for blended fuel, a 1 to 14 percent improvement in the brake thermal efficiencies over methane was found. Larsen and Wallace (1997) and Cattelan and Wallace (1994) tested a turbocharged 3.1L V6 engine under mid and high load conditions with a 15 percent H2 hythane blend and found similar trends (for the exhaust concentrations in ppm) as the light load tests by Swain et al. (1993) and Yusuf et al. (1997). Raman et al. (1994) described lean burn and stoichiometric combustion tests with a three-way catalyst. For the lean burn (5.7L GM V8) engine it was again shown that hydrogen extends the lean limit of natural gas, thereby enabling lower NOx emissions without excessive THC. When the BMEP advantage of hythane is sacrified by retarding the spark advance until methane and hythane produce equal BMEP, the NOx concentrations drop significantly. Bell and Gupta (1997) described tests with lean mixtures of natural gas blended with 5, 1, and 15 percent hydrogen on a 4 cylinder 2.5L GM engine at 22 rpm and 5 percent WOT.Again the subject of the research was to extend the lean operating limit of the engine and to investigate the performance and emissions characteristics of the SI engine at these conditions. At the natural gas lean operating limit λ =1.56 (φ =.64) hydrogen addition allowed an increase in power (up to 47 percent again with 15 percent H2) due to an increase in the average flame speed maintaining a sufficient heat release rate for good combustion quality Brake thermal efficiencies (15 percent H2) were higher than for the other fuelling cases at corresponding equivalence ratios..» During the last years, also a number of fleet testings were carried on. The recent Hythane ((24.8% vol. Hydrogen, Frank Lynch, Hydrogen Components, Inc., HCI), bus demonstration project at Sunline transit in California used a 7% hydrogen by energy formula and the NOx emissions were reduced by 5%. Based on success with Hythane buses, and the cost-effectiveness of Hythane compared to available fuel cell technology, a number of projects are currently carried on all around the world, like the Beijing Hythane Bus Projet, whose demonstration phase will be to adapt 3 natural gas engines for Hythane operation. In Sweden, operation with Hythane and natural gas had been compared for a heavy-duty natural gas engine and the study had revealed a small increase in efficiency. Subsequently, a couple of buses had been tested on the road with blend with a 8% hydrogen content (by volume). Tests during full load and constant load demonstrated a 2-3% reduction in HCemissions and higher power with mixture. Transients bring to 5% less emissions both for HC and CO but a 5% increase of NOx. From the energy point of view, there is a 14% fuel reduction. EXPERIMENTAL SET UP In the framework of an EU Interreg IIIC project called BONG-HY (parallel application of Blends Of Natural Gas and Hydrogen in internal combustion engines and fuel cells) bench tests on a natural gas vehicle had been carried on in one lab of the Casaccia Reasearch Center of ENEA. The main Italian partners involved in the project had been the Municipality of Brescia (lead partner), ASM SPA (the energy multiutility of Brescia), the Catholic University of Brescia, the Universities of Rome Tor Vergata and La Sapienza and ENEA. The light duty commercial vehicle under test had been a Daily, belonging to the ASM fleet, that had been mainly modified in the control system (ECU) for the test. Its engine was a 2.8 L NG fuelled, manufactured by IVECO (see Tab.2 for specifications). Tab.2 Engine specifications Displaced volume 28 cm 3 Compression ratio 12.2 Bore 94.4 mm Stroke 1 mm Rated power Rpm Max Torque Rpm Emission Standard Euro III The roller bench comes from APICOM; its control system has been recently upgraded by Assing. The cycle adopted for the characterisation had been the urban part of NEDC (repeated at least 2 times) and the value for the vehicle mass had been set to 35 kg; therefore the test had been more severe than the homologation one. Therefore, the results are not directly comparable with OEM data, but surely more significative for the guide cycle of the ASM vehicles that could use these blends in the future (waste collecting vehicles). Engine ECU Tuning tool Fig.4 The tool used to modify the engine maps is called RACE2, elaborated by Dimensione Sport. This software is able to transform data contained in the original eprom in easily modificable electronic mapping. Along with the software cited above, the MET16 simulator, able to modify the spark advance, the injection time and other parameters instantaneously, had been used too. The programming of the final EPROM had been obtained thanks to the EMP21 EPROM programmer produced by Needham s Electronics.

4 MEASUREMENT SYSTEM measures, they were weighed before and after drive tests (ECE 15) on our roller bench that lasted a significative time. Cylinder pressure A single cylinder head had been equipped with a piezo-electric pressure transducer hosted on a special spark plug and signals had been processed by a twochannel amplyfier while the angular position had been measured with a inductive crank-angle calculator module for on-line indicating measurements. The equipment had been manufactured by AVL, all data had been collected by a Yokogawa DL 716 digital scope. In the picture below, an example (15 r.p.m., 5 % at medium loads) of preliminary testing with pure methane is given, for the engine model validation. EXPERIMENTS Fig.7 Emissions Fig.5 Emissions had been measured using a HORIBA OBS-13 integrated system. This is composed by a MEXA-117HNDIR (Dispersive Infra-red Detectors) that measures in real time CO, CO2 and HC and by a MESA-72NOx (ZrO2 technology), for the evaluation of nitric oxides concentrations and air-fuel-ratio (AFR); furthermore, a heated flowmeter (pitot type) mounted on the sampling probe permits to calculate the mass ( see Fig. 6). Fuel Consumption Two blends had been tested, characterised by 1 and 15% by volume in hydrogen (HCNG1 and HCNG15) and used as a fuel for the urban part of the ECE-15 driving cycle. Pure methane of certified composition and certified mixtures had been used for the tests. For characterization tests, single cylinders had been used. To assure the requested precision with regards to energy consumption The main parameters that had been investigated are lambda (with values of 1 and 1.4), different spark advance angles and different values for the enrichment of the blends during transients. As main exhaust parameter which had been considered as a constraint that had not to be overcome in case of stoichiometric set up is NOx emission. Actually, hydrogen addition implies a higher laminar combustion speed and this causes an increase of combustion temperature and therefore higher NOx emissions. On the contrary, CO and HC emissions are always lower, thanks both to the lower quantity of carbon and to the improved combustion process. For lean-burn mixtures, not only NOx, but also HC monitoring had been a decisive parameter that had been taken into consideration. Actually, also HC emissions can raise due to the fact that laminar combustion speed decreases remarkably. This produces a not complete oxidation of HC. Moreover higher gas cooling during expansion delays the fuel oxidation, in particularly near cylinder s walls and in the most hidden parts of the combustion chamber. The first tests using mixtures to feed the engine, carried without any modification of the injection control map, had confirmed the foreseen NOx emissions increase related to the increasing combustion speed. This fact had required a modification of the spark ignition time. In Fig. 8 it is possible to see that a spark advance reduction of only 3 degrees (which means a little retard compared to the case of pure methane) brings to a large decrease of NOx emissions, without torque reduction.

5 9 7 RESULTS NOx ppm NOx Torque Torque Nm In the following pictures the obtained values of the first 6 months of lab tests for both the fuel consumption and the pollutants and CO 2 emissions (for different operating conditions) are represented. Figures 11 and 12 shows fuel consumption and CO 2 emissions for different hydrogen contents in HCNG while Fig. 13 represents the local emissions for the same blends Advance variation degree Fig.8 2, 15, Fuel and CO2 reduction, % Notwithstanding the above reported spark ignition time correction, engine performances with methanehydrogen blends had remained not acceptable during ECE driving cycle in terms of emissions, due to the too high NOx emission values, compared to methane. A more detailed examination of the engine behaviour during transients shows that fuel enrichment (as mapped in ECU) had been too low, therefore actual λ reaches values comprised between As a result, NOx emissions had increased too much. For this reason, a map correction has been adopted for acceleration phases. This had been allowed by a dedicated function of electronic injection unit. In this way it had been possible to decrease NOX emissions to desired values, lower than figures obtained with methane ( see Fig.9). For a lean burn blend, research of better AFR (we wanted to reach a value of 1 ppm, the same of pure methane) was limited from λ= 1 to λ= 1,45. Furthermore, the increase of AFR values causes very important power losses, as shown in Fig. 1. Therefore, λ=1,45 had been the maximum value initially fixed (this value substantially reduces NOx) and a series of tests had been produced changing the spark ignition advance to optimize the control strategy in order to increase the performances. Unfortunately, NOx had grown in an exponential way, while power gain hadn t been significative. It had also been decided that it is more convenient to adopt a lower AFR value without changing the spark advance instead of setting a high λ together with optimal advance timing. NOx ppm Lambda Fig.1 Nox Torque Torque Nm % % 1, 5,, 12, 1, 8, 6, 4, 2,, HCNG1 λ=1 HCNG1 λ=1,4 HCNG15 λ=1 HCNG15 λ=1,4 Fuel reduction Fig. 11 CO2 reduction Energy saving, % HCNG1 λ=1 HCNG1 λ=1,4 HCNG15 λ=1 HCNG15 λ=1,4 CONCLUSIONS Fig. 12 The analysis of the results of the lab tests can be considered encouraging for the continuation of the activities, even if the tests had just covered a short period of time (a few months). It s well known that the reduction of fuel consumption brings to the enhancement of the pollutants and greenhouses emissions; therefore, the optimum condition can be found dealing with the problem with different approaches, i.e. with the use of lean blends in the first case ( for the fuel consumption reduction) and with the use of stoichiometric blends in the second case ( emissions reduction). Actually, these two approaches correspond to the different conceptual ideas adopted by VOLVO (whose engines are mounted on the urban buses of the Malmo Hythane project ) and by IVECO (the manufacturer of the DAILY vehicle used for our experimentations) for the realisation of their natural gas motorisation. In our case, dealing with an IVECO engine, that had been designed in order to work in stoichiometric conditions, the adoption of a lean combustion strategy had brought us to unsatisfactory results: actually, since no changements in the engine hardware had been made, as for example the compression ratio

6 enhancement and/or the engine overfuelling, with respect to the vehicle s behaviour, a reduction of the engine specific power had been verified, beyond to the reduction of the power due to the inferior energy content in volume ( - 11% for the blend with a 15% hydrogen content by volume). Though, for both the combustion strategies adopted, the vehicle had succeeded in doing the urban cycle, the engine had worked regularly and the obtained results had been encouraging in terms of both consumptions reduction and pollutants and CO 2 emission reduction as demonstrated even by the foreign lab and road tests. The pollutants emission reduction had been very promising mainly working in stoichiometric conditions. Finally, even considering the Swedish works ( that don t present problems of power losses with the use of blends) we can say that, starting from the existent motorisations, the strategies that have to be adopted for the modifications must be coherent with the base constructor philosophy; in our case, we had taken into consideration the IVECO philosophy. Consequently, we consider the obtained results with stoichiometric conditions as the base results of a possible development of the project that foresees the field experimentation of vehicles with an IVECO motorisation (for example, industrial vehicles for the transports of goods or waste collecting vehicles). In this framework, the reduction of the energetic consumptions increases with blends with a 15% hydrogen content by volume, in a way more than proportional with the increase of hydrogen content, while for the pollutants emissions a significative difference between the use of blends with a 1% or 15% hydrogen content by volume hadn t been verified. REFERENCES [1] The Sustainable Mobility Project, Mobility 23: Meeting the challenges to sustainability, World Business Council for Sustainable Development, Switzerland, 25 [2] Riddell, B., Malmo Hydrogen and CNG/Hydrogen filling station and Hythane bus project, Carl Bro Energiekonsult AB, Sweden, 24 [3] Tunestal P., Einewall P., Stenlaas O., Johansson B., Possible short term introduction of hydrogen as vehicle fuel/fuel additive, P. Duret and Editions Technip, Paris, 24, [4] Karner D., Francfort J., Freedom car & vehicle technologies program Advanced vehicle testing activity- Arizona public service- Alternative fuel (Hydrogen) pilot plant, US DOE, 23 [5] F. Linch, Hythane: a bridge to an ultraclean renewable hydrogen energy system, Atti del Workshop IEA in Denver, 1991 [6] James Cannon, Paving the way to Natural Gas Vehicles, INFORM, Inc., 1993 [7] R. Sierens, E. Rosseel, Variable Composition Hydrogen/Natural Gas mixtures for increased engine efficiency and decreased emissions, Journal of Engineering for Gas turbines and Power, 2, [8] Hoekstra R. L., Collier, K and Mulligan N., Demonstration of Hydrogen Mixed Gas Vehicles, Proceedings, 1 th World Hydrogen Energy Conference, Cocoa Beach, Vol. 3, anno 1994 [9] Hoekstra R. L., Van Blarigan P., and Mulligan N., NOx emissions and efficiency of Hydrogen, Natural Gas and Hydrogen/Natural Gas blended fuels, SAE Paper 96113, 1996 [1] Swain M. R., Yusuf M., Dulger Z., and Swain M. N., The effects of hydrogen addition on natural gas engine operation, SAE Paper , 23 [11] Larsen J. F., and Wallace J. S., Comparison of emissions and efficiency of a turbocharged lean-burn natural gas and hythane-fuelled engine, ASME Journal of Engineering for gas turbines and power, Vol. 119, 1997 [12] Yusuf M., Swain M. R., Swain M. N., and Dulge Z., An approach to lean burn natural gas fuelled engine through hydrogen addition, Proceedings, 3 th ISATA Conference, Florence, paper 97EL81, 1997 [13] Raman V., Hansel J., Fulton J., Lynch F., and Bruderly D., Hythane an ultraclean transportation fuel, Proceedings, 1 th World Hydrogen Energy Conference, Cocoa Beach Vol. 3, pp , 1994 [14] Bell S. R., and Gupta M., Extension of the lean operating limit for natural gas fuelling of a spark ignited engine using hydrogen blending, Combustion Science and Technology, Vol. 123, pp , 1997

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8 NOx ppm NOx After NOx before Speed After Speed Before Vehicle Speed Km/h Time s. -1 Fig. 9 1,2 Emissions, g/km 1,,8 g/km,6,4,2, NG HCNG1 λ=1 HCNG1 λ=1,4 HCNG15 λ=1 HCNG15 λ=1,4 CO HC NOX Fig. 13