91快活林

Most engineering research and experiments devote significant effort to modelling and simulation of complicated phenomena and processes. We are dedicated to devising improved laser-based measurement techniques, fundamental modelling and computational simulation in order to better understand and influence engine performance.

We have developed auto-ignition models, investigated the applicability of advanced mathematical techniques and theories on vortex rings, in addition to conducting modelling on jet instabilities and fuel droplet evaporation.

Our numerical simulation of gas exchange processes to assess the feasibility of two and four stroke engine configuration for gasoline engine downsizing led to key discoveries relating to significant improvements in thermal efficiency and reduced carbon dioxide emissions.

With over 20 years of progressive research within this area, we improve understanding about gasoline sprays in our quest to produce engines, which offer improved fuel economy and lower emissions without compromising performance. Collaborating with Ricardo, we have used a problem-through-to-solution approach to study key challenges in engine performance and advance technical knowledge. Using the optical research engines located at the Sir Harry Ricardo Laboratories offers greatly improved optical access to processes.

Our team has reported on in-cylinder and fuel spray measurements. Our findings contributed to multi-national original equipment manufacturer (OEM) engine development programmes, such as the twin mechanical variable lift engine (TMVL) and controlled auto-ignition/homogeneous charge compression ignition (CAI/HCCI) concepts and led to the replacement of port fuel injection (PFI) with direct injection DI in these systems for reduced emissions.

Research has also contributed to development programmes for spray-guided, direct injection (SGDI) production engines for multi-national, automotive OEM clients, developed to be compatible not only with gasoline but also for future application with ethanol and methanol blends too.

The experimental characterisation of the initial stage of diesel jet formation and primary breakup under realistic engine conditions is challenging due to the harsh environment in which they take place. This inherent complexity is compounded by the highly transient nature of the processes involved, along with the elevated velocities and the microscopic scale at which they occur. The small size and high velocities of the droplets produced through the primary and secondary breakup have made their direct visualisation particularly difficult.

Our research strives to find solutions to these issues. We use state-of-the-art equipment and devise new techniques so that we are able to measure droplets and ligaments with unrivalled accuracy. We use simultaneous micro and macroscopic imaging to ensure clear resolution and well-lit images with minimal blurring. Ultra-high-speed microscopic imaging enabled us to identify the vortex ring motion within the vapour phase and distinguish a slipstream effect, which led to a central ligament being propelled ahead of the liquid jet. This phenomenon had been reported in the literature, but had remained unexplained until our research.

In a new £1.3m EPSRC project to help design more efficient fuels, our researchers will scrutinise microscopic fuel droplets as they reach combustion chambers. Current thinking is based on the premise that droplets are spherical but new research shows that different shapes exist. The preponderance of non-spherical droplets in high-pressure fuel sprays will have an impact on processes, and our investigation in collaboration with BP and academics from Russia, Italy and France should lead towards cleaner, more efficient fuels.

Lubricant sprays are key to smooth running throughout engineering. We use practical experimentation and analytical investigation to draw meaningful conclusions from the data we generate on this topic.

Our research team is experienced in creating test conditions to replicate lubricant sprays in action. We utilise purpose-built test rigs to mimic the lubricating conditions inside large marine diesel engines to examine the in-cylinder characteristics of marine lubricants. Our findings give insight into ways in which we can improve performance.

High-resolution microscopic imaging

The direct visualisation of diesel sprays using high-resolution microscopy can give novel insight into the complex processes involved in the initial stage of spray formation.

The light source and imaging optics are optimised to produce shadowgraphic images of sprays with unprecedented sharpness. Sub-micron resolutions and ultra-short exposure times allow the observation of previously unreported shearing instabilities and the stagnation point on the tip of diesel jets.

An oblate spheroidal cap was observed for a wide range of conditions, which may consist of residual fuel from the previous injection. These findings suggest that vapourised fuel may remain trapped in the injector holes after the end of the injection process, and would support the theory that the formation of deposits in the holes of diesel injector nozzles may be linked to the degradation of such residual fuel.

Ultra high speed microscopic video

The complex interaction between the spheroidal cap and the jet that follows were observed using an ultra high-speed camera, operated at up to 50 million images per second.

Although still apparent, the spheroidal cap is much less distinguishable at evaporating conditions. At elevated in-cylinder temperatures the spheroidal cap is in vapour state, and can be observed due to the refraction of the light caused by density gradients.

A vortex ring motion within the vapour phase was identified, and resulted in a slipstream effect, which led to a central ligament being propelled ahead of the liquid jet. This phenomenon had been reported in the literature, but had remained unexplained until our research.