Energy saving from improved fuels, engine combustion, and reduced hazards.
Submitting InstitutionUniversity of Leeds
Unit of AssessmentAeronautical, Mechanical, Chemical and Manufacturing Engineering
Summary Impact TypeTechnological
Research Subject Area(s)
Engineering: Automotive Engineering, Interdisciplinary Engineering
Summary of the impact
Experimental research and computer modelling in the School of Mechanical
Engineering have been applied by engine and oil companies to reduce fuel
consumption and noxious emissions. Studies into high pressure explosions
and burn rates have helped industry improve engine efficiencies by up to
30% and contributed to the development of much improved fuels. These new
products perform better, are less environmentally damaging and have
generated new company revenues. Research into burn rates, detonations, and
large jet-flames has also informed health and safety investigations,
particularly the UK Government Inquiry into the Buncefield explosion,
providing calculations and explanations of the blast, and recommendations
on future safety controls.
The team's research has centred on theoretical, experimental and computer
modelling studies [1;i] directed at: (a) burn rate control, (b) high
pressure, `knock-free' combustion, and (c) reduction of explosion risk,
and control of jet-flames. These have resulted in better understanding of
the dynamics and mechanisms of controlled combustion (and uncontrolled
explosions). New insights have been widely accepted and applied, resulting
in improved fuels and better control of combustion in engines and
turbines, with safety features to prevent explosions and detonations.
Between 1993 and 2012, Sheppard, Bradley, Gaskell, Lawes and Burluka
conducted rigorous mathematical modelling and experimentation on flame
front propagation and auto-ignition, under different conditions, in a
number of collaborations, with Alstom [iii], British Gas [i], Jaguar Land-Rover
[iii,iv,vi], Lotus [iii], Mahle [vii], VW [ii], Ricardo [ii],
Rolls-Royce [i,iii], Sasol [viii] and Shell [i,iii,iv,vi,viii]. They
discovered new correlations between the parameters which influence the
velocity of turbulent burning, enabling the Team to model high pressure
combustion scenarios and predict the onset of knocking with greater
accuracy [2-4, 6]. The studies employed a unique facility, designed and
developed by the Team: a fan-stirred explosion bomb incorporating laser
diagnostics, pressure transducers, and high speed photography . Burluka
and Lawes improved understanding of two-phase mixing and burning
of liquid sprays and Lawes found fuel-rich aerosols burned much
faster than had been suggested previously, indicative of an additional
High pressure combustion
Although more fuel-efficient, a high burn rate in spark-ignition engines
can lead to high pressure engine `knock' — caused by auto-ignition at
reactant `hot spots'. The consequent over-pressures are highly detrimental
and can even destroy an engine. The generation of hot spots in engine
auto- ignition and the propagation of the reaction fronts were studied
throughout the period by Sheppard and Burluka .
Parallel direct numerical simulations embodying detailed chemical kinetics
were initiated by Bradley with Morley, of Shell, and Gu, of the
Daresbury Laboratory. These simulations, combined with extensive engine
research, revealed that increased pressure can create particularly
damaging and spasmodic `super-knock' . Since 2008, collaborations with
both Shell and Aramco, revealed "super-knock" to be associated with an
unexpected gas-phase pre-ignition, an important discovery which has led to
studies on the auto-ignition characteristics of lubricating oil .
The Leeds/Shell collaboration demonstrated fundamental limitations in the
international criterion for engine knock — the octane number — for the
higher temperatures and pressures in modern engines. The simulations
showed that the complex relationships between the different physicho-chemical
parameters can be combined into a single dimensionless group,
indicative of the severity of hot spot pressure pulses. Sharpe
[5:v], showed the group was also indicative of the stability of detonation
fronts. This gave rise to a new universal parameter, the Chi-number, now
being adopted rapidly by the wider community.
Jet-flames and explosion risk
The stretched turbulent premixed flame model of Bradley and Gaskell
 was further developed, to explore the structural detail of large
jet-flames. These range from burning pools of fuel to supersonic jets. The
model revealed the correlating parameters for the height of jet-flames and
their thermal powers. In explosions in ducts, premixed flame modelling and
fan-stirred bomb research showed that, as turbulence increases, because of
increasing localised flame extinctions the turbulent burning velocity,
after increasing to a maximum value, subsequently declines. This
determines whether the shock wave generated by the accelerating flame is
strong enough to promote auto-ignition and a possible detonation,
characterised by the Chi-number.
D Bradley (Research Professor 1992-present)
PH Gaskell (Senior Lecturer 1991-96, Professor of Fluid Mechanics
CGW Sheppard (Professor of Applied Thermodynamics 1993-retired
AA Burluka (Lecturer 1998-2009, Senior Lecturer 2009-present)
M Lawes (Lecturer 1992-2000, Senior Lecturer 2000-present)
GJ Sharpe (Principal Research Fellow 2005-2008, Reader 2008-2013).
References to the research
1. D Bradley, PH Gaskell, XJ Gu, (1994). Application of a
Reynolds stress, stretched flamelet, mathematical model to computations of
turbulent burning velocities and comparison with experiments. Combust.
Flame, 96, 221-248.http://dx.doi.org/10.1016/0010-2180(94)90011-6
2. D Bradley, MZ Haq, RA Hicks, T Kitagawa, M Lawes, CGW
Sheppard, R Woolley, (2003). Turbulent burning velocity,
burned gas distribution and associated flame surface definition. Combust.
Flame, 133, 415-430. http://dx.doi.org/10.1016/S0010-2180(03)00039-7
3. AA Burluka, K Liu, CGW Sheppard, AJ Smallbone, R
Woolley, (2004). "The influence of simulated residual and NO
concentrations on knock onset for PRFs and gasolines. SAE Trans. Jour.
Fuels and Lubricants, 113(4), 873-1889.http://dx.doi.org/10.4271/2004-01-2998
Note: All Leeds researchers in bold. All of the above
publications are internationally recognised, with rigorous peer review
processes and international editorial boards, The quality of the
underpinning research being at least 2* is demonstrated by references 2, 4
and 5. Other relevant publications comprise 3 books and upwards of 98
papers, 9 of which received prizes or awards.
Key research grants
i. D Bradley, PH Gaskell. Advanced Turbulent Combustion
Modelling. EPSRC grant GR/K96212, April 96 - March 99. Liaisons with
British Gas, Ishikawajima-Narima Heavy Industries, National Power,
Rolls-Royce, Shell, Computational Combustion for Engineering Applications
ii. CGW Sheppard, (PI), M Lawes, AA Burluka, R
Woolley. Gasoline Engine Turbo-charging: Advanced Gasoline Powertrain for
reduced fuel consumption. EU contracts G3RD-CT-2000- 00364 (GET-CO2),
£595,200, and G3RD-CT-2002-00789 (GET-DRIVE), Jan 01 - Dec 05. In
collaboration with Ricardo Consulting Engineers, UK and VW, Germany,
iii. M Lawes, (PI), D Bradley, R Woolley. Fundamental
engine fuel studies at intermediate and high pressures & temperatures.
EPSRC grant GR/S70203/01, July 04 - Jun 07. In collaboration with Alstom
Power UK, Jaguar Cars, Lotus Engineering, Rolls-Royce and Shell Global
iv. CGW Sheppard, (PI), M Lawes, AA Burluka, D Bradley,
R Woolley. Combustion Concepts For Sustainable Premium Vehicles. EPSRC
grant GR/S58843/01, Oct 03-Sept 07. In collaboration with Jaguar Cars and
Shell Global Solutions, £299,314.
v. GJ Sharpe, (PI). Ignition, propagation and failure of
detonations and deflagration-to-detonation transition. Oct 2005- Dec 2009.
EPSRC Advanced Fellowship GR/S49513/02, £160,408.
vi. AA Burluka, (PI), CGW Sheppard. UltraBoost for
Economy. TSB grant BN008E, Aug 2010 - Aug 2013. In collaboration with JLR,
Shell, GE Precision, Univ. of Bath, Imperial College, £142,676.
vii. AA Burluka, (PI). Autoignition in strongly boosted engines.
DHPA award with Mahle Powertrain UK, Oct 2010 - Oct 2013, £92,000.
viii. GJ Sharpe, (PI), CGW Sheppard M Lawes, D Bradley,
J Griffiths. Collaborative Research in Energy with South Africa:
Fundamental Characterisation of Autoignition and Flame Propagation of
Synthetic Fuels. EPSRC grant EP/G068933/1, Apr 2009. In collaboration with
SASOL Technology, South Africa, and Shell Global Solutions, UK, £396,550.
All Engineering and Physical Sciences Research Council (EPSRC),
Technology Strategy Board (TSB) and European project grants are
peer-reviewed and evaluated on stringent quality criteria.
Details of the impact
Much progress has been made in developing high pressure, knock-resistant,
engines through a range of industrial collaborations with high value
returns. In parallel, the Team's fundamental studies have made major
contributions to reductions in fire and explosion hazards throughout the
automotive, aviation, and energy sectors.
Energy efficient engines.
Engines with high burn rates are generally cleaner and more efficient,
provided knock is avoided. As a result of extensive collaborations with
Jaguar Land-Rover (JLR), Lotus, Rolls-Royce (R-R), and VW, the Leeds
experimental and modelling insights into burning rates have had a
widespread influence on reciprocating engine and gas turbine design. The
R-R collaboration led to improved igniters and prevention of high-altitude
flame-out in aero-turbines, as well as the prevention of auto-ignition and
flash-back in land-based turbines. A long term collaboration with JLR [A]
and, latterly, GE Precision Engineering [B] has led to improved control of
fuel/air mixing, ignition, burn rates, and knock suppression, together
with reductions in the uncontrolled variations in working cycles. The
Leeds computer modelling code was incorporated by JLR into its internal
engine system modelling packages [A]. These fundamental improvements in
the design and engineering of the companies' engines [A,B] have
contributed to their development, in the UK, of commercially very
successful, high pressure, knock-free, turbo-charged, engines. These are
characterised by their reduced size, yet with higher power, combined with
consequent impressive improvements in efficiency and reductions in
emissions. Both of these savings amount to up to approximately 30% of
previous values [A]. Since 2010, collaborations to this end were
consolidated in the UltraBoost project [vi], which included JLR, GE
Precision, Shell, the Universities of Bath and Imperial College, with
Leeds making its major contributions in the key area of
carefully-controlled high pressure combustion, just short of the knock
limit. JLR has invested £355M to manufacture the engines into production
[C] and has created 10,700 new jobs in UK since 2008. Data in [D] indicate
the huge savings from even a 1% improvement in efficiency.
Energy efficient fuels
The detailed observations and modelling of high-pressure combustion and
auto-ignition, not only showed the widely used Octane Number criteria to
be misleading for modern engines, but it also led to the development of
alternative design approaches [E]. These, combined with fuel tests in the
Leeds bomb, supported Shell's development of a new vehicle fuel formula
with increased burn rate and minimised auto-ignition [F]. This world-wide
FuelSave range, launched in 2010, improved engine efficiency by up to 2%,
with consequent reduction in carbon emissions. Specialist support was
given also to the development of Shell's Formula One fuels and
fuel-blending laws with Sasol.
Fuel explosions — contributions to inquiries and safety
Following the vapour cloud explosion at Buncefield oil storage terminal
in 2005, Bradley was asked to advise the late Lord Newton's Major
Incident Investigation Board [G] into the Buncefield disaster, through
membership of its Explosion Mechanism Group. Findings from the Leeds Team,
along with input from others members of the expert group, were used to
explain the cause and damage from this huge explosion [H]. From this
assessment of the explosion dynamics, the Inquiry recommended specific
measures to prevent a recurrence [G]. The introduction of new safety
standards, site layouts and technologies [F], informed in part from a
scientific understanding of the explosion, has had a significant impact
for the UK. The new safety measures will have helped to avert a similar
explosion which had a total economic cost of around £1billion [G]. The
implementation cost of all the recommendations was calculated at
approximately £82M, with an estimated benefit through the reduction of
risk "in the region of £162million" [G].
The Team's jet-flame model has been used in the important area of flare
design by Shell [F] and validated in tests at the South West Research
Institute. The Team's correlation of jet-flame data, with parameters drawn
from the computer model, is invaluable for estimating the magnitude of oil
field blow-outs, and designing non-polluting flares. After Bradley's
earlier involvement in the Concorde fire Inquiry, Qinetiq asked him to use
the Leeds jet-flame model to quantify upstream fuel leaks from the
observed sizes of the fire plume from the Nimrod aircraft over
Afghanistan. This confirmed magnitudes of fuel leakage after in-flight
re-fueling. The subsequent Haddon-Cave Report [I] resulted in the Nimrod
being withdrawn from service, averting the possibility of further crashes
and potential loss of life.
Impact on Society, Culture and Creativity
The stretched turbulent flame codes are freely available and are being
used by other groups. They are embodied in the THOR fluid dynamics code of
the Daresbury Laboratory, developed in collaboration with the Leeds group.
The Team contributed to BBC programmes, for radio on oil field blow-outs
and for TV on the Olympic flame (2012). The findings on the limitations of
Octane Numbers have had international repercussions throughout the
automotive and oil industries.
Sources to corroborate the impact
A. Statement from Manager, Research, Jaguar Land Rover, regarding
B. Statement from Technical Director, GE Precision Engineering, regarding
C. JLR invests £355M in UK low emissions engine plant.
plant/ website accessed and saved 19.10.13
D. Digest of UK Energy Statistics, Department of Energy and Climate
Change, Energy consumption in the United Kingdom: 2012.Chapter 1, Energy.
2012-exc-cover.pdf Website accessed and saved. 28.8.13.
E. Statement from Senior Research Science Consultant, Aramco, regarding
octane number limitations and new approaches.
F. Statement from Technology Manager, Fuel Science, Shell Global
Solutions, regarding development of new fuels, safety, jet flames.
G. Buncefield Major Incident Investigation Board, "The Buncefield
Incident 11 December 2005 Final Report", Volumes 1 and 2, Crown Copyright,
H. Statement from Chief Technical Advisor to European Commission,
regarding all aspects of Buncefield explosion.
I. Charles Haddon-Cave QC, (2009). "An independent review into the
broader issues surrounding the loss of the RAF Nimrod MR2Aircraft XV230 in
Afghanistan in 2006." Ordered by the House of Commons.
Website accessed and saved 28.8.13.