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Exhaust Heat Utilisation and Losses in Internal Combustion Engines with Focus on the Gas Exchange System
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Exhaust gas energy recovery should be considered in improving fuel economy of internal combustion engines. A large portion of fuel energy is wasted through the exhaust of internal combustion engines. Turbocharger and turbocompound can, however, recover part of this wasted heat. The energy recovery depends on the efficiency and mass flow of the turbine(s) as well as the exhaust gas state and properties such as pressure, temperature and specific heat capacity. The exhaust gas pressure is the principal parameter which is required for the turbine energy recovery, but higher exhaust back-pressures on the engines create higher pumping losses. This is in addition to the heat losses in the turbochargers what makes any measurement and simulation of the engines more complex.

This thesis consists of two major parts. First of all, the importance of heat losses in turbochargers has been shown theoretically and experimentally with the aim of including heat transfer of the turbochargers in engine simulations. Secondly, different concepts have been examined to extract exhaust heat energy including turbocompounding and divided exhaust period (DEP) with the aim of improved exhaust heat utilisation and reduced pumping losses.

In the study of heat transfer in turbochargers, the turbocharged engine simulation was improved by including heat transfer of the turbocharger in the simulation. Next, the heat transfer modelling of the turbochargers was improved by introducing a new method for convection heat transfer calculation with the support of on-engine turbocharger measurements under different heat transfer conditions. Then, two different turbocharger performance maps were assessed concerning the heat transfer conditions in the engine simulation. Finally, the temperatures of turbocharger’s surfaces were predicted according to the measurements under different heat transfer conditions and their effects are studied on the turbocharger performance. The present study shows that the heat transfer in the turbochargers is very crucial to take into account in the engine simulations, especially in transient operations.

In the study of exhaust heat utilisation, important parameters concerning turbine and gas exchange system that can influence the waste heat recovery were discussed. In addition to exhaust back-pressure, turbine speed and turbine efficiency, the role of the air-fuel equivalence ratio was demonstrated in details, because lower air-fuel equivalence ratio in a Diesel engine can provide higher exhaust gas temperature. The results of this study indicate that turbocompound engine efficiency is relatively insensitive to the air-fuel equivalence ratio.

To decrease the influence of the increased exhaust back-pressure of a turbocompound engine, a new architecture was developed by combining the turbocompound engine with DEP. The aim of this study was to utilise the earlier phase (blowdown) of the exhaust stroke in the turbine(s) and let the later phase (scavenging) of the exhaust stroke bypass the turbine(s). To decouple the blowdown phase from the scavenging phase, the exhaust flow was divided between two different exhaust manifolds with different valve timing.

According to this study, this combination improves the fuel consumption in low engine speeds and deteriorates it at high engine speeds. This is mainly due to long duration of choked flow in the exhaust valves because this approach is using only one of the two exhaust valves on each cylinder at a time.

Therefore, the effects of enlarged effective flow areas of the exhaust valves were studied. Two methods were used to enlarge the effective flow area i.e. increasing the diameters of the blowdown and scavenging valves by 4 mm; and modifying the valve lift curves of the exhaust valves to fast opening and closing. Both methods improved BSFC in the same order even though they were different in nature. Fast opening and closing of the exhaust valves required shorter blowdown duration and longer scavenging duration. The modified lift curves provided less pumping losses, less available energy into the turbine and larger amplitude of the pulsating flow through the turbine.

In order for defining a set of important parameters that should be examined in experimental studies, a sensitivity analysis was performed on the turbocompound DEP engine in terms of break specific fuel consumption to different parameters concerning the gas exchange such as blowdown valve timing, scavenging valve timing, blowdown valve size, scavenging valve size, discharge coefficients of blowdown and scavenging ports, turbine efficiency, turbine size and power transmission efficiency.

Finally, to overcome the restriction in the effective flow areas of the exhaust valves, DEP was implemented externally on the exhaust manifold instead of engine exhaust valves, which is called externally DEP (ExDEP). This innovative engine architecture, which benefits from supercharging, turbocharging and turbocompounding, has a great fuel-saving potential in almost all load points up to 4%.

Abstract [sv]

Avgasenergiåtervinning bör övervägas för att förbättra förbränningsmotorers bränsleekonomi. En stor del av bränslets energi förloras via förbränningsmotorernas avgaser. Dock kan turbo och turbocompound återvinna en del av denna värmeförlust. Energiåtervinningen beror på verkningsgraden och massflödet genom turbinen (erna), liksom avgasernas tillstånd och egenskaper, såsom tryck, temperatur och specifik värmekapacitet. Avgastrycket är den viktigaste parametern som påverkar turbinenergiåtervinningen, men högre avgasmottryck skapar högre pumpförluster. Detta utöver värmeförlusterna i turboaggregator gör mätning och simulering av motorer komplexa.

Avhandlingen består av två huvuddelar. Först har vikten av värmeförluster i turboladdare visats både teoretiskt och experimentellt, med syfte att införa värmeöverföring av turboladdare i motorsimuleringar. För det andra, har olika koncept undersökts för att utvinna avgasvärmeenergi med turbocompound och delad avgasperiod (DEP), i syfte att förbättra avgasvärmeutnyttjande och minska pumpförluster.

I studien av värmeöverföring i turboladdare förbättrades turbomotorsimulering genom att inkludera värmeöverföring av turboladdaren i simuleringen. Härnäst förbättrades värmeöverföringsmodelleringen av turboladdarna genom att införa en ny metod för konvektiv värmeöverföringsberäkning, med stöd av mätningar på turbon på motorn, under olika förutsättningar för värmeöverföring. Därefter bedömdes två olika turboaggregats prestandamappar för värmeöverföringsförhållandena i motorsimulering. Slutligen beräknades temperaturerna på turbons ytor, baserat på mätningarna, under olika värmeöver­föringsförhållanden och effekterna studerades på turboprestanda. Den aktuella studien visar att värmeöverföringen i turboladdarna är mycket viktigt att ta hänsyn till i motor simuleringarna, speciellt i transienter.

I studien av avgasvärmets utnyttjande, undersöktes viktiga parametrar med avseende på turbinen och gasväxlingen, som kan påverka värmeåtervinningen. Förutom avgasmottryck, turbinvarvtal och turbinverkningsgrad, visades påverkan av luft-bränsleförhållandet, eftersom lägre luft-bränsleförhållandet i en dieselmotor kan ge högre avgastemperatur. Resultaten av denna studie indikerar att turbocompoundmotorns verkningsgrad är ganska okänslig för luft-bränsleförhållandet.

För att minska påverkan av det ökade avgasmottrycket hos en turbokompoundmotor, utvecklades en ny arkitektur genom att kombinera turbokompoundmotorn med DEP. Syftet med denna studie var att utnyttja den tidiga fasen (blowdown) av avgastakten i turbinen (erna) och låta den senare fasen (scavenging) av avgastakten gå förbi turbinen (erna). För att frikoppla blowdown fasen från scavenging fasen delades avgasflödet upp mellan två olika avgasgrenrör med olika ventiltider.

Enligt denna studie, förbättrar denna kombination bränsleförbrukningen vid låga varvtal och försämrar den på höga varvtal. Detta är främst på grund av lång varaktighet av kritiskt flöde i avgasventilerna eftersom DEP använder endast en av de två avgasventilerna på varje cylinder i taget.

Därför studerades effekten av förstorade effektiva flödesareor hos avgasventilerna. Två metoder användes för att förstora den effektiva flödesarean, ökning diametrarna av blowdown och scavenging ventilerna med 4 mm och ändring av avgasventillyftkurvorna till snabb öppning och snabb stängning. Båda metoderna förbättrades BSFC i samma storleksordning trots att de var av olika slag. Snabb öppning och stängning av avgasventilerna krävde kortare blowdownvaraktighet och längre scavengingvaraktighet. De modifierade lyftkurvorna gav mindre pumpförluster, mindre tillgänglig energi in i turbinen och större amplitud av pulserande flöde genom turbinen.

För att definiera en uppsättning viktiga parametrar som bör undersökas i experimentella studier, genomfördes en känslighetsanalys på turbocompound DEP motorn i fråga om specifik bränsleförbrukning som funktion av olika parametrar som rör gasväxling såsom blowdown ventiltider, scavenging ventiltider, blowdown ventilstorlek, scavenging ventilstorlek, strömningskoefficienterna hos blowdown och scavenging kanalerna, turbinverkningsgrad, turbinstorlek och kraftöverföringsverkningsgraden.

Slutligen, för att övervinna begränsningar av de effektiva flödesareorna hos avgasventilerna genomfördes DEP externt i avgasgrenröret i stället för att utnyttja avgasventilerna, här kallad externt DEP (ExDEP). Denna innovativa motorarkitektur, som drar nytta av överladdning, turboladdning och turbocompound, har en stor bränslesparande potential, i nästan alla belastningspunkter upp till 4%.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. , xiv, 101 p.
Series
TRITA-MMK, ISSN 1400-1179 ; 2014:07
Keyword [en]
Turbocharger, heat transfer, heat loss, exhaust heat utilisation, waste heat recovery, turbocompound, divided exhaust period, internal combustion engine, gas exchange, pumping loss, variable valve timing, WHR, DEP
Keyword [sv]
Turbo, värmeöverföring, värmeförluster, avgasvärme utnyttjande, förluster vid värmeåtervinning, turbocompound, delad avgasperiod, förbränningsmotor, gasväxling, pumpningsförlust, variabla ventiltider, WHR, DEP
National Category
Applied Mechanics Energy Engineering Vehicle Engineering
Research subject
Vehicle and Maritime Engineering; Energy Technology
Identifiers
URN: urn:nbn:se:kth:diva-152520ISBN: 978-91-7595-279-6 (print)OAI: oai:DiVA.org:kth-152520DiVA: diva2:750114
Public defence
2014-10-30, F3, Lindstedsvägen 26, KTH, Stockholm, 14:00 (English)
Opponent
Supervisors
Funder
Swedish Energy Agency, F6432
Note

QC 20141001

Available from: 2014-10-01 Created: 2014-09-26 Last updated: 2015-08-26Bibliographically approved
List of papers
1. Improving Turbocharged Engine Simulation by Including Heat Transfer in the Turbocharger
Open this publication in new window or tab >>Improving Turbocharged Engine Simulation by Including Heat Transfer in the Turbocharger
2012 (English)In: 2012 SAE International, SAE international , 2012Conference paper, Published paper (Refereed)
Abstract [en]

Engine simulation based on one-dimensional gas dynamics is well suited for integration of all aspects arising in engine and power-train developments. Commonly used turbocharger performance maps in engine simulation are measured in non-pulsating flow and without taking into account the heat transfer. Since on-engine turbochargers are exposed to pulsating flow and varying heat transfer situations, the maps in the engine simulation, i.e. GT-POWER, have to be shifted and corrected which are usually done by mass and efficiency multipliers for both turbine and compressor. The multipliers change the maps and are often different for every load point. Particularly, the efficiency multiplier is different for every heat transfer situation on the turbocharger. The aim of this paper is to include the heat transfer of the turbocharger in the engine simulation and consequently to reduce the use of efficiency multiplier for both the turbine and compressor. A set of experiment has been designed and performed on a water-oil-cooled turbocharger, which was installed on a 2 liter GDI engine with variable valve timing, for different load points of the engine and different conditions of heat transfer in the turbocharger. The experiments were the base to simulate heat transfer on the turbocharger, by adding a heat sink before the turbine and a heat source after the compressor. The efficiency multiplier of the turbine cannot compensate for all heat transfer in the turbine, so it is needed to put out heat from the turbine in addition to the using of efficiency multiplier. Results of this study show that including heat transfer of turbocharger in engine simulation enables to decrease the use of turbine efficiency multiplier and eliminate the use of compressor efficiency multiplier to correctly calculate the measured gas temperatures after turbine and compressor.

Place, publisher, year, edition, pages
SAE international, 2012
Keyword
Turbocharger, Heat Transfer, Turbocharged Engine, Simulation
National Category
Vehicle Engineering Energy Engineering Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-70200 (URN)2-s2.0-84877171285 (Scopus ID)
Conference
SAE 2012 World Congress & Exhibition, April 24-26, 2012, Detroit, Michigan, USA
Projects
On-Engine Turbocharger Performance
Note

QS 2012

Available from: 2012-04-24 Created: 2012-01-30 Last updated: 2016-12-22Bibliographically approved
2. Turbocharged SI-Engine Simulation with Cold and Hot-Measured Turbocharger Performance Maps
Open this publication in new window or tab >>Turbocharged SI-Engine Simulation with Cold and Hot-Measured Turbocharger Performance Maps
2012 (English)In: Proceedings of ASME Turbo Expo 2012, Vol 5, ASME Press, 2012, 671-679 p.Conference paper, Published paper (Refereed)
Abstract [en]

Heat transfer within the turbocharger is an issue in engine simulation based on zero and one-dimensional gas dynamics. Turbocharged engine simulation is often done without taking into account the heat transfer in the turbocharger. In the simulation, using multipliers is the common way of adjusting turbocharger speed and parameters downstream of the compressor and upstream of the turbine. However, they do not represent the physical reality. The multipliers change the maps and need often to be different for different load points. The aim of this paper is to simulate a turbocharged engine and also consider heat transfer in the turbocharger. To be able to consider heat transfer in the turbine and compressor, heat is transferred from the turbine volute and into the compressor scroll. Additionally, the engine simulation was done by using two different turbocharger performance maps of a turbocharger measured under cold and hot conditions. The turbine inlet temperatures were 100 and 600°C, respectively. The turbocharged engine experiment was performed on a water-oil-cooled turbocharger (closed waste-gate), which was installed on a 2-liter gasoline direct-injected engine with variable valve timing, for different load points of the engine. In the work described in this paper, the difference between cold and hot-measured turbocharger performance maps is discussed and the quantified heat transfers from the turbine and to/from the compressor are interpreted and related to the maps.

Place, publisher, year, edition, pages
ASME Press, 2012
Keyword
Turbocharger, Heat transfer, Performance Map, Turbocharged Engine
National Category
Energy Engineering Aerospace Engineering Vehicle Engineering Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-70231 (URN)10.1115/GT2012-68758 (DOI)000324956100070 ()2-s2.0-84881241280 (Scopus ID)978-079184471-7 (ISBN)
Conference
ASME Turbo Expo 2012: Turbine Technical Conference and Exposition, GT 2012; Copenhagen; Denmark; 11 June 2012 through 15 June 2012
Projects
On-Engine Turbocharger Performance
Note

QC 20131106

Available from: 2012-03-09 Created: 2012-01-30 Last updated: 2014-10-01Bibliographically approved
3. Temperature Estimation of Turbocharger Working Fluids and Walls under Different Engine Loads and Heat Transfer Conditions
Open this publication in new window or tab >>Temperature Estimation of Turbocharger Working Fluids and Walls under Different Engine Loads and Heat Transfer Conditions
2013 (English)In: SAE Technical Papers, 2013Conference paper, Published paper (Refereed)
Abstract [en]

Turbocharger performance maps, which are used in engine simulations, are usually measured on a gas-stand where the temperatures distributions on the turbocharger walls are entirely different from that under real engine operation. This should be taken into account in the simulation of a turbocharged engine. Dissimilar wall temperatures of turbochargers give different air temperature after the compressor and different exhaust gas temperature after the turbine at a same load point. The efficiencies are consequently affected. This can lead to deviations between the simulated and measured outlet temperatures of the turbocharger turbine and compressor. This deviation is larger during a transient load step because the temperatures of turbocharger walls change slowly due to the thermal inertia. Therefore, it is important to predict the temperatures of turbocharger walls and the outlet temperatures of the turbocharger working fluids in a turbocharged engine simulation.

In the work described in this paper, a water-oil-cooled turbocharger was extensively instrumented with several thermocouples on reachable walls. The turbocharger was installed on a 2-liter gasoline engine that was run under different loads and different heat transfer conditions on the turbocharger by using insulators, an extra cooling fan, radiation shields and water-cooling settings. The turbine inlet temperature varied between 550 and 850 °C at different engine loads.

The results of this study show that the temperatures of turbocharger walls are predictable from the experiment. They are dependent on the load point and the heat transfer condition of the turbocharger. The heat transfer condition of an on-engine turbocharger could be defined by the turbine inlet temperature, ambient temperature, oil heat flux, water heat flux and the velocity of the air around the turbocharger. Thus, defining the heat transfer condition and rotational speed of the turbocharger provides temperatures predictions of the turbocharger walls and the working fluids. This prediction enables increased precision in engine simulation for future work in transient operation.

Series
SAE Technical Papers, ISSN 0148-7191
Keyword
Turbocharger, Heat transfer, Temperature estimation
National Category
Vehicle Engineering Energy Engineering Fluid Mechanics and Acoustics Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-127531 (URN)10.4271/2013-24-0123 (DOI)2-s2.0-84890375940 (Scopus ID)
Conference
11th International Conference on Engines and Vehicles, ICE 2013; Capri, Naples, Italy, 15-19 September 2013
Funder
Swedish Energy Agency
Note

QC 20140109

Available from: 2013-08-30 Created: 2013-08-30 Last updated: 2014-10-01Bibliographically approved
4. Evaluation of different heat transfer conditions on an automotive turbocharger
Open this publication in new window or tab >>Evaluation of different heat transfer conditions on an automotive turbocharger
2014 (English)In: International Journal of Engine Research, ISSN 1468-0874, E-ISSN 2041-3149, Vol. 16, no 2, 137-151 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents a combination of theoretical and experimental investigations for determining the main heat fluxes within a turbocharger. These investigations consider several engine speeds and loads as well as different methods of conduction, convection, and radiation heat transfer on the turbocharger. A one-dimensional heat transfer model of the turbocharger has been developed in combination with simulation of a turbocharged engine that includes the heat transfer of the turbocharger. Both the heat transfer model and the simulation were validated against experimental measurements. Various methods were compared for calculating heat transfer from the external surfaces of the turbocharger, and one new method was suggested.

The effects of different heat transfer conditions were studied on the heat fluxes of the turbocharger using experimental techniques. The different heat transfer conditions on the turbocharger created dissimilar temperature gradients across the turbocharger. The results show that changing the convection heat transfer condition around the turbocharger affects the heat fluxes more noticeably than changing the radiation and conduction heat transfer conditions. Moreover, the internal heat transfers from the turbine to the bearing housing and from the bearing housing to the compressor are significant, but there is an order of magnitude difference between these heat transfer rates.

Place, publisher, year, edition, pages
Sage Publications, 2014
Keyword
Turbocharger, Heat transfer, On-engine turbocharger, Heat flux, Convection
National Category
Applied Mechanics Energy Engineering Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-143535 (URN)10.1177/1468087414524755 (DOI)000349225300002 ()2-s2.0-84921873306 (Scopus ID)
Funder
Swedish Energy Agency
Note

QC 20140923

Available from: 2014-03-24 Created: 2014-03-24 Last updated: 2017-12-05Bibliographically approved
5. A review of turbocompounding as a waste heat recovery system for internal combustion engines
Open this publication in new window or tab >>A review of turbocompounding as a waste heat recovery system for internal combustion engines
2015 (English)In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 49, 813-824 p.Article in journal (Refereed) Published
Abstract [en]

Internal combustion engines waste a large amount of fuel energy through their exhausts. Various technologies have been developed for waste heat recovery such as turbocompounds, Rankine bottoming cycles, and thermoelectric generators that reduce fuel consumption and CO2 emissions. Turbocompounding is still not widely applied to vehicular use despite the improved fuel economy, lower cost, volume, and complexity higher exhaust gas recirculation driving capability and improved transient response. This paper comprehensively reviews the latest developments and research on turbocompounding to discover important variables and provide insights into the implementation of a high-efficiency turbocompound engine. Attention should be paid to the optimization of turbocompound engines and their configurations because the major drawback of this technology is additional exhaust back-pressure, which leads to higher pumping loss in the engines. Applying different technologies and concepts on turbocompound engines makes the exhaust energy recovery more efficient and provides more freedom in the design and optimization of the engines. Turbine efficiency plays an important role in the recovery of the wasted heat so turbine design is a crucial issue in turbocompounding. In addition, variability in geometry and rotational speed of power turbines allows for more efficient turbocompound engines in different operating conditions. The conclusion drawn from this review is that turbocompounding is a promising technology for reducing fuel consumption in the coming decades in both light- and heavy-duty engines.

Keyword
Internal combustion engine, Turbocompound, Waste heat recovery
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-152687 (URN)10.1016/j.rser.2015.04.144 (DOI)000357141900064 ()2-s2.0-84929998005 (Scopus ID)
Funder
Swedish Energy Agency
Note

QC 20150826. Updated from Manuscript to Article in journal.

Available from: 2014-10-01 Created: 2014-10-01 Last updated: 2017-12-05Bibliographically approved
6. Demonstration of Air-Fuel Ratio Role in One-Stage Turbocompound Diesel Engines
Open this publication in new window or tab >>Demonstration of Air-Fuel Ratio Role in One-Stage Turbocompound Diesel Engines
2013 (English)In: SAE Technical Papers, 2013, Vol. 11Conference paper, Published paper (Refereed)
Abstract [en]

A large portion of fuel energy is wasted through the exhaust of internal combustion engines. Turbocompound can, however, recover part of this wasted heat. The energy recovery depends on the turbine efficiency and mass flow as well as the exhaust gas state and properties such as pressure, temperature and specific heat capacity.

The main parameter influencing the turbocompound energy recovery is the exhaust gas pressure which leads to higher pumping loss of the engine and consequently lower engine crankshaft power. Each air-fuel equivalence ratio (λ) gives different engine power, exhaust gas temperature and pressure. Decreasing λ toward 1 in a Diesel engine results in higher exhaust gas temperatures of the engine.  λ can be varied by changing the intake air pressure or the amount of injected fuel which changes the available energy into the turbine. Thus, there is a compromise between gross engine power, created pumping power, recovered turbocompound power and consumed compressor power.

In this study, the effects of different λ values and exhaust back-pressure have been investigated on the efficiency of a heavy-duty Diesel engine equipped with a single-stage electric turbocompounding. A one-dimensional gas dynamics model of a turbocharged engine was utilized that was validated against measurements at different load points. Two configurations of turbocompound engine were made. In one configuration an electric turbocharger was used and the amount of fuel was varied with constant intake air pressure. In another configuration the turbocharger turbine and compressor were disconnected to be able to control the turbine speed and the compressor speed independently; then the compressor pressure ratio was varied with constant engine fuelling and the exhaust back-pressure was optimized for each compressor pressure ratio.

At each constant turbine efficiency there is a linear relation between the optimum exhaust back-pressure and ideally expanded cylinder pressure until bottom dead center with closed exhaust valves. There is an optimum λ for the turbocharged engine with regard to the fuel consumption. In the turbocompound engine, this will be moved to a richer λ that gives the best total specific fuel consumption; however, the results of this study indicates that turbocompound engine efficiency is relatively insensitive to the air-fuel ratio.

Series
SAE Technical Papers, ISSN 0148-7191 ; Vol. 11
Keyword
Turbocompound, Diesel engine, Waste heat recovery, Air-fuel ratio
National Category
Vehicle Engineering Energy Engineering Applied Mechanics Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-139145 (URN)10.4271/2013-01-2703 (DOI)2-s2.0-84890377517 (Scopus ID)
Conference
SAE/KSAE 2013 International Powertrains, Fuels and Lubricants Meeting, FFL 2013; Seoul, South Korea, 21-23 October 2013
Funder
Swedish Energy Agency
Note

QC 20140108

Available from: 2014-01-08 Created: 2014-01-07 Last updated: 2014-10-01Bibliographically approved
7. The Exhaust Energy Utilization of a Turbocompound Engine Combined with Divided Exhaust Period
Open this publication in new window or tab >>The Exhaust Energy Utilization of a Turbocompound Engine Combined with Divided Exhaust Period
2014 (English)Conference paper, Published paper (Refereed)
Abstract [en]

To decrease the influence of the increased exhaust pressure of a turbocompound engine, a new architecture is developed by combining the turbocompound engine with divided exhaust period (DEP). The aim of this study is to utilize the earlier stage (blowdown) of the exhaust stroke in the turbine(s) and let the later stage (scavenging) of the exhaust stroke bypass the turbine(s). To decouple the blowdown phase from the scavenging phase, the exhaust flow is divided between two different exhaust manifolds with different valve timing. A variable valve train system is assumed to enable optimization at different load points. The fuel-saving potential of this architecture have been theoretically investigated by examining different parameters such as turbine flow capacity, blowdown valve timing and scavenging valve timing. Many combinations of these parameters are considered in the optimization of the engine for different engine loads and speeds.

This architecture produces less negative pumping work for the same engine load point due to lower exhaust back pressure; however, the exhaust mass flow into the turbine(s) is decreased. Therefore, there is a compromise between the turbine energy recovery and the pumping work. According to this study, this combination shows fuel-saving potential in low engine speeds and limitations at high engine speeds. This is mainly due to the choked flow in the exhaust valves because this approach is using only one of the two exhaust valves at a time. To reveal the full potential of this approach, increasing the effective flow area of the valves should be studied.

National Category
Applied Mechanics Vehicle Engineering Energy Engineering
Identifiers
urn:nbn:se:kth:diva-143204 (URN)000347841100015 ()978-0-081000-34-2 (ISBN)978-0-081000-33-5 (ISBN)
Conference
11th International Conference on Turbochargers and Turbocharging; London, ENGLAND, MAY 13-14, 2014
Projects
turbocompound, divided exhaust period, engine
Note

QC 20141001

Available from: 2014-03-18 Created: 2014-03-18 Last updated: 2015-02-18Bibliographically approved
8. Effects of Effective Flow Areas of Exhaust Valves on a Turbocompound Diesel Engine Combined With Divided Exhaust Period
Open this publication in new window or tab >>Effects of Effective Flow Areas of Exhaust Valves on a Turbocompound Diesel Engine Combined With Divided Exhaust Period
2014 (English)In: Proceedings from the FISITA 2014 World Automotive Congress, 2014Conference paper, Published paper (Refereed)
Abstract [en]

Research and /or Engineering Questions/Objective: Exhaust gas energy recovery in internal combustion engines is one of the key challenges in the future developments. The objective of this study is to reveal the fuel-saving potential of a turbocompound Diesel engine combined with divided exhaust period (DEP). The exhaust flow is provided for two different manifolds via separate valves, blowdown and scavenging, at different timings. The main challenge in this combination is choked flow through the exhaust valves due to the restricted effective flow areas. Therefore, the effects of enlarged effective flow areas of the exhaust valves are studied.

Methodology: A commercial 1D gas dynamics code, GT-POWER, was used to simulate a turbocharged Diesel engine which was validated against measurements. Then the turbocharged engine model was modified to a turbocompound engine with DEP. Using statistical analysis in the simulation (design of experiment), the performance of this engine was studied at different sizes, lift curves and timings of the exhaust valves and turbine swallowing capacity.

Results: In the paper the effects of the effective flow areas of the exhaust valves are presented on the break specific fuel consumption, pumping mean effective pressure and the turbine energy recovery by increasing the valve size and modifying valve lift curve to fast opening and closing. This has been done in a low engine speed and full load. The main finding is that the flow characteristics of the exhaust valves in the turbocompound DEP engine are very important for gaining the full efficiency benefit of the DEP concept.  The turbocompound DEP engine with modified valve lift shape of the exhaust valves could improve the overall brake specific fuel consumption by 3.44% in which 0.64% of the improvement is due to the valve lift curve. Modified valve lift curves contribute mainly in decreasing the period of choked flow through the exhaust valves.

Limitations of this study: The simulations were not validated against measurements; however, the mechanical and geometrical limitations were tried to keep realistic when manipulating the valve flow area events.

What does the paper offer that is new in the field in comparison to other works of the author: In addition to the novelty of the engine architecture that combines turbocompound with DEP, the statistical analysis and comparison presented in this paper is new especially with demonstrating the importance of crank angle coupled flow characteristics of the valves.

Conclusion: To achieve full fuel-saving potential of turbocompound DEP engines, the flow characteristics of the exhaust valves must be considered. The effective flow areas of the exhaust valves play important roles in the choked flow through the valves, the pumping work and the brake specific fuel consumption of the engine.

National Category
Applied Mechanics Vehicle Engineering Energy Engineering
Identifiers
urn:nbn:se:kth:diva-143208 (URN)
Conference
the FISITA 2014 World Automotive Congress held in Maastricht, the Netherlands from 02-06 June
Note

QC 20150202

Available from: 2014-03-18 Created: 2014-03-18 Last updated: 2015-02-02Bibliographically approved
9. Performance Sensitivity to Exhaust Valves and Turbine Parameters on a Turbocompound Engine with Divided Exhaust Period
Open this publication in new window or tab >>Performance Sensitivity to Exhaust Valves and Turbine Parameters on a Turbocompound Engine with Divided Exhaust Period
2014 (English)In: SAE International Journal of Engines, ISSN 1946-3936, E-ISSN 1946-3944, Vol. 7, no 4, 1722-1733 p.Article in journal (Refereed) Published
Abstract [en]

Turbocompound can utilize part of the exhaust energy on internal combustion engines; however, it increases exhaust back pressure, and pumping loss.  To avoid such drawbacks, divided exhaust period (DEP) technology is combined with the turbocompound engine. In the DEP concept the exhaust flow is divided between two different exhaust manifolds, blowdown and scavenging, with different valve timings. This leads to lower exhaust back pressure and improves engine performance.

Combining turbocompound engine with DEP has been theoretically investigated previously and shown that this reduces the fuel consumption and there is a compromise between the turbine energy recovery and the pumping work in the engine optimization. However, the sensitivity of the engine performance has not been investigated for all relevant parameters. The main aim of this study is to analyze the sensitivity of this engine architecture in terms of break specific fuel consumption to different parameters concerning the gas exchange such as blowdown valve timing, scavenging valve timing, blowdown valve size, scavenging valve size, discharge coefficients of blowdown and scavenging ports, turbine efficiency, turbine size and power transmission efficiency. This study presents the sensitivity analysis of the turbocompound DEP engine to these parameters and defines a set of important parameters that should be examined in experimental studies.

Place, publisher, year, edition, pages
SAE, 2014
Keyword
Turbocomopund engine, divided exhaust period, sensitivity, exhaust valves, turbine
National Category
Vehicle Engineering Applied Mechanics Energy Engineering
Research subject
Machine Design; Vehicle and Maritime Engineering; Energy Technology
Identifiers
urn:nbn:se:kth:diva-149333 (URN)
Conference
SAE 2014 International Powertrains, Fuels and Lubricants Meeting,October 20-23, 2014,Birmingham, United Kingdom
Projects
WHR
Funder
Swedish Energy Agency
Note

QC 20140901

The paper is updated from Conference paper to Article in Journal. QC 20141118

Available from: 2014-08-20 Created: 2014-08-20 Last updated: 2017-12-05Bibliographically approved
10. Externally divided exhaust period on a turbocompound engine for fuel-saving
Open this publication in new window or tab >>Externally divided exhaust period on a turbocompound engine for fuel-saving
2014 (English)Conference paper, Published paper (Other academic)
Abstract [en]

To improve exhaust heat utilization of a turbocharged engine, divided exhaust period (DEP) and turbocompound are integrated. The DEP concept decreases pumping loss created by the turbocompound. In the DEP concept the exhaust flow is divided between two different exhaust manifolds, blowdown and scavenging. One of the two exhaust valves on each engine cylinder is opened to the blowdown manifold at the first phase of exhaust stroke and the other valve is opened to the scavenging manifold at the later phase of exhaust stroke. This leads to lower exhaust back pressure and pumping loss. The combination of turbocompound engine with DEP has been examined previously and the result showed that this combination reduces the fuel consumption in low engine speeds and deteriorates it in high engine speeds. The main restriction of this combination was the low effective flow areas of the exhaust valves at high engine speeds.

To overcome this restriction and increase the effective flow areas of the exhaust valves, DEP is employed externally on the exhaust manifold instead of engine exhaust valves. In externally DEP (ExDEP), both exhaust valves will be opened and closed similar to the corresponding turbocharged engine and the exhaust flow is divided by flow splits on the exhaust manifold. Two valves on the outlet ports of each flow split are added. One of them is a non-return valve (check valve) and the other one is synchronized with the cam shaft.

In this study, the fuel-saving potential of ExDEP is analysed on the turbocompound engine at different engine speeds and loads and compared with the corresponding turbocharged engine, turbocompound engine and turbocompound DEP engine equipped. The results show that ExDEP has a great fuel-saving potential in almost all load points.

ExDEP concept, itself, is a novel concept that there is no available literature about it. Moreover, combination of this new gas exchange system with turbocompound engines is an innovative extension of combined turbocompound DEP engines.

Keyword
Externally divided exhaust period, turbocompound, engine
National Category
Applied Mechanics Energy Engineering Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-152689 (URN)
Conference
9th International MTZ Conference, Heavy-Duty, On- and Off-Highway Engines,18 November 2014 - 19 November 2014, Saarbrücken
Projects
WHR
Funder
Swedish Energy Agency
Note

QC 20141119

Available from: 2014-10-01 Created: 2014-10-01 Last updated: 2014-11-19Bibliographically approved

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