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Erdgas und Flüssiggas in kolbenmotorischer Diesel-Gas-Zweistoffverbrennung

Brennverlaufsanalyse, Emission, Mehrfachdieselinjektion, sequentielle Gaseindüsung, Abgasrückführung und Drall
BuchKartoniert, Paperback
207 Seiten
Deutsch
AbstractThe reduction of carbon dioxide emissions is discussed by politicians as well as ingeneral public today. The efforts that are taken are not limited to Germany or Europe,but take place in most parts of the world. In terms of vehicle propulsion combustionengines contribute a noteworthy part of the worldwide CO2-emission.The present thesis was intended to investigate the CO2-reduction potentials ofgaseous fuels used in a combined diesel-gas-combustion on the basis of state-ofthe-art Diesel engines and their control systems.As gaseous fuels both compressed natural gas (CNG) as well as liquefied petroleumgas (LPG) were used. Due to their lower carbon ratio, they provide a potential ofreducing CO2 by 11% (LPG) and 24% (CNG) if combusted with an equal effectiveefficiency compared to Diesel engines.Former investigations on the sector of the diesel-gas-combustion were made on thebasis of diesel engines that are almost not state-of-the-art today. These engineswere equipped with mechanical systems for dosing diesel and gas and were not oronly low-turbocharged. These investigations showed the feasibility of this type ofcombined combustion, but also identified a strongly increasing emission of hydrocarbonsand a decrease of the engine´s efficiency. Investigations for improving theseeffects were implemented by varying the diesel injection timing as well as throttlingthe air mass flow to lower the air fuel ratio.Today s state-of-the-art diesel engines are equipped with electronically controlleddiesel injection systems that allow multiple injections per stroke and operate with highinjection pressures. Furthermore cooled exhaust gas recirculation systems (EGR) aswell as flaps for influencing the air inlet swirl can be used to affect the combustion.Additionally, electronic control devices allow realizing a cylinder selective andsequentially operating gas dosing.Therefore, the present investigation is focusing in its experimental part on thereduction of CO2- and HC-emissions by using all available state-of-the-art air, dieseland gas control devices. In its theoretical part, a modified method for analyzing thediesel-gas-combustion was developed. This calculation method shows a goodreproducibility and comparability among the three research engines that were used.The engines are all six cylinder diesel engines. Two of them belong to the heavy dutysector; one is a passenger car engine. In a first step the aim was to check whetherthe correlations that are known from literature can be transferred to state-of-the-artengines. The results for the engine M1 (electronically controlled inline injection pump)and M2 (CommonRail Injection system) showed an enormous increase ofhydrocarbon (factor 29 for engine M1 and 25 for M2) and carbon monoxide (factor 13for M1 and 2.5 for M2) emission while increasing the energetic gas ratio up to 70%.II AbstractAt the same time particle emissions could be reduced by 80% in maximum and thecarbon dioxide emissions, depending on the operating point, by 24%.The increase of HC and CO can be explained by lean air fuel ratios in the air-gasphasesthat lead on the one hand to an expiration of the flame (so called flamequenching) and on the other hand to unburned air-gas-areas at the outer zone of thecombustion chamber near to the wall (wall quenching). Simultaneously thecombustion center was delayed by several degCS, what is, besides the increase ofunburned fuel, the second reason for increasing specific fuel consumption bymaximum 4%. In total, these results correspond to those that are described inliterature, so it can be noted that these main relations are valid for state-of-the-artdiesel engines too.While increasing the gas rate the particle concentration drops down. One new resultof this work is represented by the result that the particle spectrum always stays withinthe spectrum of reference diesel combustion, so that a shifting of the particlespectrum to smaller particles that might easier enter the lungs can be excluded.At the same time on engine M2 cylinder pressure gradients could be significantlyreduced compared to a single diesel operation. Although special acoustic measurementswere not carried out, the noise reduction could be clearly observed.With respect to the aspired emission certification of the engines M1 and M3, somestudent assistant investigations were conducted that specially focused on theimprovement of the diesel-gas-combustion regarding an optimization of the dieselmain injection timing, whereas the focus of this thesis was put on the interaction ofdiesel-gas-combustion with modern engine control systems.The engine´s load showed a big influence on fuel consumption and emissions. HCand CO emissions decrease significantly with higher loads. The fuel consumption incombined diesel-gas-combustion at very low loads of for example 2bar is slightlyhigher than in diesel operation, but converges for increasing loads. At 10bar the fuelconsumption of the DG-combustion is even 1% lower than in diesel mode.Concerning the CO2-emissions the diesel-gas-combustion enables a reduction ofmaximum 16% at medium and high loads compared to diesel combustion only.Further investigations concerning a variable air management via throttle as well as aturbocharger with variable turbine geometry show that there is a potential to reducehydrocarbon emission by a factor 2.5 and carbon monoxide by a factor 2. The maineffect is that lower air fuel ratios lead to a postponement of the combustion from thefirst combustion section (phase of pre-mixed fuels) to the second one (phase ofdiesel metering) due to an increased ignition delay time.For the first time the present work reveals the interactional effects of a multiple dieselinjection and diesel gas combustion. The quantity of an early pilot injection (PiI2) anda pilot injection close to TDC (PiI1) shows a typical NOx-particle-trade-off at mediumAbstract IIIgas parts and part load. An important new finding is that an early timing of both pilotinjections leads to a reduction of nitrogen oxides and particles simultaneously. At thesame time the pilot injection that is close to TDC (PiI1) which leads to the ignition ofthe air-gas-mixture can be used to uncouple the beginning of the gas combustionfrom the diesel main injection.Detailed investigations concerning exhaust gas recirculation and inlet swirl show thattheir effects still remain independent from each other also for combined diesel-gascombustion.EGR can be distinctively used to decrease nitrogen oxide emissions bymaximum 60% at part load while particle emission increases following a typical NOxparticle-trade-off. HC and CO emissions increase by maximum 20 respectively 30%whereas the fuel consumption (-4%) and the CO2-emission could be reduced (-7%).The increase of efficiency results from a shorte-ning of the ignition delay time and ade-throttling due to EGR.The inlet swirl at part load shows an optimum regarding all emission for medium flappositions. An increase of inlet turbulences reduces especially hydrocarbon andcarbon monoxide emissions so that it can be used to control their behavior in a mixeddiesel-gas-application. Furthermore the inlet swirl system can be applied to move onthe typical NOx-particle-trade-off on a lower absolute level than without.As a further control system a cylinder selective and sequentially operating gas dosingunit was investigated. Used for combined diesel-gas-combustion, a reduction ofhydrocarbons by 35% in comparison to a centrally dosing gas system can berealized, whereas all other limited emissions were kept neutral or also reduced.All the results from the different subsystems (air and EGR management, inlet swirlsystem and cylinder selective and sequentially operating gas dosing) built the basisfor in total three emission certifications on the engines M1 and M3. Whereas thediesel-LPG application for M3 without any additional oxidation catalyst only allowedlow maximum gas parts up to 34%, the diesel-CNG certification for M1 with anadditional methane selective oxidation catalyst leads to medium energetic gas ratiosof 56% and a large average CO2-reduction by 13%.The present thesis may also be the basis for further research in the field of combineddiesel-gas-combustion. Visual analysis of the combustion as well as mechanicaloptimization of the combustion chamber and the camshaft timing will reveal morepotential to reduce CO2-emissions. Also the potential of a direct gas injection and thecombination of all presented technologies will be worth to investigate.At the same time the question comes up whether the results can be also transferredto other engine applications. For example engines in block heat power plants mightbe diesel-gas-engines that can manage changing fuel availability by a variableenergetic fuel mix of gas and a liquid fuel.mehr

Produkt

KlappentextAbstractThe reduction of carbon dioxide emissions is discussed by politicians as well as ingeneral public today. The efforts that are taken are not limited to Germany or Europe,but take place in most parts of the world. In terms of vehicle propulsion combustionengines contribute a noteworthy part of the worldwide CO2-emission.The present thesis was intended to investigate the CO2-reduction potentials ofgaseous fuels used in a combined diesel-gas-combustion on the basis of state-ofthe-art Diesel engines and their control systems.As gaseous fuels both compressed natural gas (CNG) as well as liquefied petroleumgas (LPG) were used. Due to their lower carbon ratio, they provide a potential ofreducing CO2 by 11% (LPG) and 24% (CNG) if combusted with an equal effectiveefficiency compared to Diesel engines.Former investigations on the sector of the diesel-gas-combustion were made on thebasis of diesel engines that are almost not state-of-the-art today. These engineswere equipped with mechanical systems for dosing diesel and gas and were not oronly low-turbocharged. These investigations showed the feasibility of this type ofcombined combustion, but also identified a strongly increasing emission of hydrocarbonsand a decrease of the engine´s efficiency. Investigations for improving theseeffects were implemented by varying the diesel injection timing as well as throttlingthe air mass flow to lower the air fuel ratio.Today s state-of-the-art diesel engines are equipped with electronically controlleddiesel injection systems that allow multiple injections per stroke and operate with highinjection pressures. Furthermore cooled exhaust gas recirculation systems (EGR) aswell as flaps for influencing the air inlet swirl can be used to affect the combustion.Additionally, electronic control devices allow realizing a cylinder selective andsequentially operating gas dosing.Therefore, the present investigation is focusing in its experimental part on thereduction of CO2- and HC-emissions by using all available state-of-the-art air, dieseland gas control devices. In its theoretical part, a modified method for analyzing thediesel-gas-combustion was developed. This calculation method shows a goodreproducibility and comparability among the three research engines that were used.The engines are all six cylinder diesel engines. Two of them belong to the heavy dutysector; one is a passenger car engine. In a first step the aim was to check whetherthe correlations that are known from literature can be transferred to state-of-the-artengines. The results for the engine M1 (electronically controlled inline injection pump)and M2 (CommonRail Injection system) showed an enormous increase ofhydrocarbon (factor 29 for engine M1 and 25 for M2) and carbon monoxide (factor 13for M1 and 2.5 for M2) emission while increasing the energetic gas ratio up to 70%.II AbstractAt the same time particle emissions could be reduced by 80% in maximum and thecarbon dioxide emissions, depending on the operating point, by 24%.The increase of HC and CO can be explained by lean air fuel ratios in the air-gasphasesthat lead on the one hand to an expiration of the flame (so called flamequenching) and on the other hand to unburned air-gas-areas at the outer zone of thecombustion chamber near to the wall (wall quenching). Simultaneously thecombustion center was delayed by several degCS, what is, besides the increase ofunburned fuel, the second reason for increasing specific fuel consumption bymaximum 4%. In total, these results correspond to those that are described inliterature, so it can be noted that these main relations are valid for state-of-the-artdiesel engines too.While increasing the gas rate the particle concentration drops down. One new resultof this work is represented by the result that the particle spectrum always stays withinthe spectrum of reference diesel combustion, so that a shifting of the particlespectrum to smaller particles that might easier enter the lungs can be excluded.At the same time on engine M2 cylinder pressure gradients could be significantlyreduced compared to a single diesel operation. Although special acoustic measurementswere not carried out, the noise reduction could be clearly observed.With respect to the aspired emission certification of the engines M1 and M3, somestudent assistant investigations were conducted that specially focused on theimprovement of the diesel-gas-combustion regarding an optimization of the dieselmain injection timing, whereas the focus of this thesis was put on the interaction ofdiesel-gas-combustion with modern engine control systems.The engine´s load showed a big influence on fuel consumption and emissions. HCand CO emissions decrease significantly with higher loads. The fuel consumption incombined diesel-gas-combustion at very low loads of for example 2bar is slightlyhigher than in diesel operation, but converges for increasing loads. At 10bar the fuelconsumption of the DG-combustion is even 1% lower than in diesel mode.Concerning the CO2-emissions the diesel-gas-combustion enables a reduction ofmaximum 16% at medium and high loads compared to diesel combustion only.Further investigations concerning a variable air management via throttle as well as aturbocharger with variable turbine geometry show that there is a potential to reducehydrocarbon emission by a factor 2.5 and carbon monoxide by a factor 2. The maineffect is that lower air fuel ratios lead to a postponement of the combustion from thefirst combustion section (phase of pre-mixed fuels) to the second one (phase ofdiesel metering) due to an increased ignition delay time.For the first time the present work reveals the interactional effects of a multiple dieselinjection and diesel gas combustion. The quantity of an early pilot injection (PiI2) anda pilot injection close to TDC (PiI1) shows a typical NOx-particle-trade-off at mediumAbstract IIIgas parts and part load. An important new finding is that an early timing of both pilotinjections leads to a reduction of nitrogen oxides and particles simultaneously. At thesame time the pilot injection that is close to TDC (PiI1) which leads to the ignition ofthe air-gas-mixture can be used to uncouple the beginning of the gas combustionfrom the diesel main injection.Detailed investigations concerning exhaust gas recirculation and inlet swirl show thattheir effects still remain independent from each other also for combined diesel-gascombustion.EGR can be distinctively used to decrease nitrogen oxide emissions bymaximum 60% at part load while particle emission increases following a typical NOxparticle-trade-off. HC and CO emissions increase by maximum 20 respectively 30%whereas the fuel consumption (-4%) and the CO2-emission could be reduced (-7%).The increase of efficiency results from a shorte-ning of the ignition delay time and ade-throttling due to EGR.The inlet swirl at part load shows an optimum regarding all emission for medium flappositions. An increase of inlet turbulences reduces especially hydrocarbon andcarbon monoxide emissions so that it can be used to control their behavior in a mixeddiesel-gas-application. Furthermore the inlet swirl system can be applied to move onthe typical NOx-particle-trade-off on a lower absolute level than without.As a further control system a cylinder selective and sequentially operating gas dosingunit was investigated. Used for combined diesel-gas-combustion, a reduction ofhydrocarbons by 35% in comparison to a centrally dosing gas system can berealized, whereas all other limited emissions were kept neutral or also reduced.All the results from the different subsystems (air and EGR management, inlet swirlsystem and cylinder selective and sequentially operating gas dosing) built the basisfor in total three emission certifications on the engines M1 and M3. Whereas thediesel-LPG application for M3 without any additional oxidation catalyst only allowedlow maximum gas parts up to 34%, the diesel-CNG certification for M1 with anadditional methane selective oxidation catalyst leads to medium energetic gas ratiosof 56% and a large average CO2-reduction by 13%.The present thesis may also be the basis for further research in the field of combineddiesel-gas-combustion. Visual analysis of the combustion as well as mechanicaloptimization of the combustion chamber and the camshaft timing will reveal morepotential to reduce CO2-emissions. Also the potential of a direct gas injection and thecombination of all presented technologies will be worth to investigate.At the same time the question comes up whether the results can be also transferredto other engine applications. For example engines in block heat power plants mightbe diesel-gas-engines that can manage changing fuel availability by a variableenergetic fuel mix of gas and a liquid fuel.