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Divided Exhaust Period on Heavy-Duty Diesel Engines
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Due to growing concerns regarding global energy security and environmental sustainability it is becoming increasingly important to increase the energy efficiency of the transport sector. The internal combustion engine will probably continue to be the main propulsion system for road transportation for many years to come. Hence, much effort must be put in reducing the fuel consumption of the internal combustion engine to prolong a future decline in fossil fuel production and to reduce greenhouse gas emissions.

Turbocharging and variable valve actuation applied to any engine has shown great benefits to engine efficiency and performance. However, using a turbocharger on an engine gives some drawbacks. In an attempt to solve some of these issues and increase engine efficiency further this thesis deals with the investigation of a novel gas exchange concept called divided exhaust period (DEP). The core idea of the DEP concept is to utilize variable valve timing technology on the exhaust side in combination with turbocharging. The principle of the concept is to let the initial high energy blow-down pulse feed the turbocharger, but bypass the turbine during the latter part of the exhaust stroke when back pressure dominates the pumping work. The exhaust flow from the cylinder is divided between two exhaust manifolds of which one is connected to the turbine, and one bypasses the turbine. The flow split between the manifolds is controlled with a variable valve train system.

The DEP concept has been studied through simulations on three heavy-duty diesel engines; one without exhaust gas recirculation (EGR), one with short route EGR and one with long route EGR. Simulations show a potential improvement to pumping work, due to reduced backpressure, with increased overall engine efficiency as a result. Although, the efficiency improvement is highly dependent on exhaust valve size and configuration due to issues with choked flow in the exhaust valves. The EGR system of choice also proves to have a high impact on the working principle of the DEP application. Furthermore, the DEP concept allows better control of the boost pressure and allows the turbine to operate at higher efficiency across the whole load and speed range. The option of discarding both wastegate and variable geometry turbine is apparent, and there is little need for a twin-entry type turbine since pulse interference between cylinders is less of an issue.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , vi, 72 p.
Series
Trita-MMK, ISSN 1400-1179 ; 2013:01
National Category
Vehicle Engineering
Identifiers
URN: urn:nbn:se:kth:diva-109529ISBN: 978-91-7501-605-4 (print)OAI: oai:DiVA.org:kth-109529DiVA: diva2:583227
Presentation
2013-01-25, B319 Gladan, Brinellvägen 83, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20130108

Available from: 2013-01-08 Created: 2013-01-07 Last updated: 2013-01-08Bibliographically approved
List of papers
1. Divided Exhaust Period on Heavy-Duty Diesel Engines
Open this publication in new window or tab >>Divided Exhaust Period on Heavy-Duty Diesel Engines
2012 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Divided Exhaust Period (DEP) has previously been studied on SI engines while results fromHD diesels are scarcer. In this paper the DEP concept has been numerically simulated on two HD dieselengines; one without EGR and one with high rates of short route EGR. The aim is to reduce fuelconsumption, residual gas content and to improve boost control, while current EGR rates are maintained.

The central idea of the DEP concept is to let the initial high energy blow-down pulse feed theturbocharger, but bypass the turbine during the latter part of the exhaust stroke when back pressuredominates the pumping work. The exhaust flow from the cylinder is divided between two exhaust manifoldsof which one is connected to the turbine, and one bypasses the turbine. The flow split betweenthe manifolds is controlled with a variable valve train system.

Results show a reduction of pumping losses for both engine configurations. In the non-EGRcase, the DEP concept offers the possibility to control the mass flow and pressure ratio over the turbine.This allows the turbocharger to operate in a high efficiency mode for a wide range of engine loadpoints. For the EGR case, there is less freedom in control of turbine mass flow, since the blow-downphase is used for both turbine work and EGR flow. Therefore the fuel consumption benefit is reduced.

The conclusion of this paper is that the simulations of the DEP concept show improvements toengine performance and efficiency. In the case of high EGR rates it is shown that the EGR flow shouldnot be deducted from the blow-down phase.

National Category
Engineering and Technology Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-107725 (URN)
Conference
THIESEL 2012 Conference on Thermo- and Fluid Dynamic Processes in Direct Injection Engines
Note

QC 20130108

Available from: 2012-12-17 Created: 2012-12-17 Last updated: 2013-01-08Bibliographically approved
2. Divided Exhaust Period: Effects of Changing the Relation between Intake, Blow-Down and Scavenging Valve Area
Open this publication in new window or tab >>Divided Exhaust Period: Effects of Changing the Relation between Intake, Blow-Down and Scavenging Valve Area
2013 (English)Conference paper, Published paper (Refereed)
Abstract [en]

In a previous paper we showed the effects of applying the Divided Exhaust Period (DEP) concept on two heavy-duty diesel engines, with and without Exhaust Gas Recirculation (EGR). Main findings were improved fuel consumption due to increased pumping work, improved boost control and reduced residual gas content. However, some limitations to the concept were discovered.  In the case of high rates of short route EGR, it was apparent that deducting the EGR flow from the turbine manifold impaired optimal valve timing strategies. Furthermore, for both of the studied engines it was clear that the size and ratio of blow-down to scavenging valve area is of paramount importance for engine fuel efficiency.

In this paper, the DEP concept has been studied together with a long route EGR system. As expected it gave more freedom to valve timing strategies when driving pressure for EGR is no longer controlled with the valve timing, as in the short route case. However, when evaluating different combinations of intake, blow-down and scavenging valve area, the optimal relation proves to be strongly dependent on the current EGR system and EGR rates. Hence, for different engine setups the trade-off between total intake and total exhaust area needs to be re-evaluated for optimal engine fuel efficiency. This paper also presents general trends in how different valve timing strategies and EGR rates affect both pumping work and boost pressure.

National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-109528 (URN)
Conference
SAE World Congress, April 16-18, 2013, Detroit, Michigan, USA
Note

QC 20130108

Available from: 2013-01-07 Created: 2013-01-07 Last updated: 2013-01-08Bibliographically approved

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