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Advancing the Limits of Dual Fuel Combustion
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

There is a growing interest in alternative transport fuels. There are two underlying reasons for this interest; the desire to decrease the environmental impact of transports and the need to compensate for the declining availability of petroleum. In the light of both these factors the Diesel Dual Fuel, DDF, engine is an attractive concept. The primary fuel of the DDF engine is methane, which can be derived both from renewables and from fossil sources. Methane from organic waste; commonly referred to as biomethane, can provide a reduction in greenhouse gases unmatched by any other fuel. The DDF engine is from a combustion point of view a hybrid between the diesel and the otto engine and it shares characteristics with both.

This work identifies the main challenges of DDF operation and suggests methods to overcome them. Injector tip temperature and pre-ignitions have been found to limit performance in addition to the restrictions known from literature such as knock and emissions of NOx and HC. HC emissions are especially challenging at light load where throttling is required to promote flame propagation. For this reason it is desired to increase the lean limit in the light load range in order to reduce pumping losses and increase efficiency. It is shown that the best results in this area are achieved by using early diesel injection to achieve HCCI/RCCI combustion where combustion phasing is controlled by the ratio between diesel and methane. However, even without committing to HCCI/RCCI combustion and the difficult control issues associated with it, substantial gains are accomplished by splitting the diesel injection into two and allocating most of the diesel fuel to the early injection. HCCI/RCCI and PPCI combustion can be used with great effect to reduce the emissions of unburned hydrocarbons at light load.

At high load, the challenges that need to be overcome are mostly related to heat. Injector tip temperatures need to be observed since the cooling effect of diesel flow through the nozzle is largely removed. Through investigation and modeling it is shown that the cooling effect of the diesel fuel occurs as the fuel resides injector between injections and not during the actual injection event. For this reason; fuel residing close to the tip absorbs more heat and as a result the dependence of tip temperature on diesel substitution rate is highly non-linear. The problem can be reduced greatly by improved cooling around the diesel injector. Knock and preignitions are limiting the performance of the engine and the behavior of each and how they are affected by gas quality needs to be determined. Based on experiences from this project where pure methane has been used as fuel; preignitions impose a stricter limit on engine operation than knock.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , v, 56 p.
Series
Trita-MMK, ISSN 1400-1179
Keyword [en]
Diesel Dual Fuel, Methane, CNG, Biogas, Injector, Coking, Knock, Pre-ignition, Preignition, HCCI, PPCI, PPC, RCCI
National Category
Vehicle Engineering
Identifiers
URN: urn:nbn:se:kth:diva-96945ISBN: 978-91-7501-427-2 (print)OAI: oai:DiVA.org:kth-96945DiVA: diva2:533308
Presentation
2012-06-15, B319 Gladan, Brinellvägen 83, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Projects
Diesel Dual Fuel
Note
QC 20120626Available from: 2012-06-26 Created: 2012-06-13 Last updated: 2012-06-26Bibliographically approved
List of papers
1. Combustion Modes in a Diesel-CNG Dual Fuel Engine
Open this publication in new window or tab >>Combustion Modes in a Diesel-CNG Dual Fuel Engine
2011 (English)In: SAE Technical Paper 2011-01-1962, 2011, Society of Automotive Engineers of Japan, Inc , 2011, 2387-2398 p.Conference paper, Published paper (Refereed)
Abstract [en]

Diesel Dual Fuel, DDF, is a concept where a combination of methane and diesel is used in a compression ignited engine, maintaining the high compression ratio of a diesel engine with the resulting benefits in thermal efficiency.

One benefit of having two fuels on board the vehicle is the additional degree of freedom provided by the ratio between the fuels. This additional degree of freedom enables control of combustion phasing for combustion modes such as Homogenous Charge Compression Ignition, HCCI, and Partly Premixed Compression Ignition, PPCI. These unconventional combustion modes have great potential to limit emissions at light load while maintaining the low pumping losses of the base diesel engine.

A series of tests has been carried out on a single cylinder lab engine, equipped with a modern common rail injection system supplying the diesel fuel and two gas injectors, placed in the intake runners. Four load points are investigated and three different types of combustion are evaluated.

The study confirmed the desirable emission characteristics of HCCI and PPCI combustion and demonstrated the potential to control the combustion phasing by utilizing all degrees of freedom provided by a common rail injection system and two fuels.

Place, publisher, year, edition, pages
Society of Automotive Engineers of Japan, Inc, 2011
Keyword
Diesel Dual Fuel, Biogas, DDF, CNG, methane, HCCI, PPC, PPCI, RCCI, Förbränningsmotorteknik, metan
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-65693 (URN)10.4271/2011-01-1962 (DOI)2-s2.0-84881193912 (Scopus ID)
Conference
JSAE Powertrains, Fuels & Lubricants
Projects
Diesel Dual Fuel
Note
QC 20120202Available from: 2012-02-02 Created: 2012-01-25 Last updated: 2014-09-15Bibliographically approved
2. Characterization and Potential of Dual FuelCombustion in a Modern Diesel Engine
Open this publication in new window or tab >>Characterization and Potential of Dual FuelCombustion in a Modern Diesel Engine
2011 (English)In: SAE Technical Paper 2011-01-2223, SAE International , 2011Conference paper, Published paper (Refereed)
Abstract [en]

Diesel Dual Fuel, DDF, is a concept which promises the possibility to utilize CNG/biogas in a compression ignition engine maintaining a high compression ratio, made possible by the high knock resistance of methane, and the resulting benefits in thermal efficiency associated with Diesel combustion.

A series of tests has been carried out on a single cylinder lab engine, equipped with a modern common rail injection system supplying the diesel fuel and two gas injectors, placed in the intake runners. One feature of port injected Dual Fuel is that full diesel functionality is maintained, which is of great importance when bringing the dual fuel technology to market. The objective of the study was to characterize and investigate the potential for dual fuel combustion utilizing all degrees of freedom available in a modern diesel engine.

Increased diesel pilot proved efficient at reducing NOx emissions at low λ. Advanced combustion phasing has the potential to extend the lean limit for operation. Stoichiometric operation using high levels of EGR is identified as a promising field in conjunction with raised inlet temperature.

Place, publisher, year, edition, pages
SAE International, 2011
Keyword
Diesel Dual Fuel, Biogas, DDF, CNG, methane, Förbränningsmotorteknik, Biogas, metan
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-65727 (URN)10.4271/2011-01-2223 (DOI)2-s2.0-84877548364 (Scopus ID)
Conference
Commercial Vehicle Engineering Congress, September 2011, Chicago
Projects
Diesel Dual Fuel
Note
QC 20120202Available from: 2012-02-02 Created: 2012-01-25 Last updated: 2014-09-15Bibliographically approved
3. Controlling the Injector Tip Temperature in a DieselDual Fuel Engine
Open this publication in new window or tab >>Controlling the Injector Tip Temperature in a DieselDual Fuel Engine
2012 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Diesel Dual Fuel, DDF, is a concept where a combination of methane and diesel is used in a compression ignited engine, maintaining the high compression ratio of a diesel engine with the resulting benefits in thermal efficiency. Attention has recently been drawn to the fact that the tip of the diesel injector may reach intolerable temperatures. The high injector tip temperatures in the DDF engine are caused by the reduction in diesel flow through the injector. For dual fuel operation, as opposed to diesel, high load does not necessarily imply a high flow of diesel through the injector nozzle.

This research investigated the factors causing high injector tip temperatures in a DDF engine and the underlying mechanisms which transfer heat to and from the injector tip. Parameter sweeps of each influential parameter were carried out and evaluated. In addition to this, a simple and useful model was constructed based on the heat balance of the injector tip.

Decreasing the thermal resistance between the injector tip and the cooling water by inserting a copper sleeve around the injector tip has the potential to greatly reduce the injector tip temperature and effectively remove it as a limiting factor.

Place, publisher, year, edition, pages
SAE International, 2012
Keyword
Diesel Dual Fuel, CNG, Methane, Biogas, Alternative fuels, injector, coking, overheating
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-96943 (URN)10.4271/2012-01-0826 (DOI)2-s2.0-84877181760 (Scopus ID)
Conference
SAE World Congress, April 24-26, 2012, Detroit, Michigan, USA
Projects
Diesel Dual Fuel
Note
QC 20120613Available from: 2012-06-13 Created: 2012-06-13 Last updated: 2014-09-15Bibliographically approved

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