Colin Copeland

Ultra Boost for Economy: Extending the Limits of Extreme Engine Downsizing

The paper discusses the concept, design and final results from the ‘Ultra Boost for Economy’ collaborative project, which was part-funded by the Technology Strategy Board, the UKs innovation agency. The project comprised industry- and academia-wide expertise to demonstrate that it is possible to reduce engine capacity by 60% and still achieve the torque curve of a modern, large-capacity naturally-aspirated engine, while encompassing the attributes necessary to employ such a concept in premium vehicles. In addition to achieving the torque curve of the Jaguar Land Rover naturally-aspirated 5.0 litre V8 engine (which included generating 25 bar BMEP at 1000 rpm), the main project target was to show that such a downsized engine could, in itself, provide a major proportion of a route towards a 35% reduction in vehicle tailpipe CO2 on the New European Drive Cycle, together with some vehicle-based modifications and the assumption of stop-start technology being used instead of hybridization. In order to do this vehicle modelling was employed to set part-load operating points representative of a target vehicle and to provide weighting factors for those points. The engine was sized by using the fuel consumption improvement targets and a series of specification steps designed to ensure that the required full-load performance and driveability could be achieved. The engine was designed in parallel with 1-D modelling which helped to combine the various technology packages of the project, including the specification of an advanced charging system and the provision of the necessary variability in the valvetrain system. An advanced intake port was designed in order to ensure the necessary flow rate and the charge motion to provide fuel mixing and help suppress knock, and was subjected to a full transient CFD analysis. A new engine management system was provided which necessarily had to be capable of controlling many functions, including a supercharger engagement clutch and full bypass system, direct injection system, port-fuel injection system, separately-switchable cam profiles for the intake and exhaust valves and wide-range fast-acting camshaft phasing devices. Testing of the engine was split into two phases. The first usied a test bed Combustion Air Handling Unit to enable development of the combustion system without the complication of a new charging system being fitted to the engine. To set boundary conditions during this part of the programme, heavy reliance was placed on the 1-D simulation. The second phase tested the full engine. The ramifications of realizing the engine design from a V8 basis in terms of residual friction versus the fuel consumption results achieved are also discussed. The final improvement in vehicle fuel economy is demonstrated using a proprietary fuel consumption code, and is presented for the New European Drive Cycle, the FTP-75 cycle and a 120 km/h (75 mph) cruise condition.

Comparison Between Steady and Unsteady Double-Entry Turbine Performance Using the Quasi-Steady Assumption

The experimental performance evaluation of a circumferentially divided, double-entry turbocharger turbine is presented in this paper with the aim of understanding the influence of pulsating flow. By maintaining a constant speed but varying the frequency of the pulses, the influence of frequency was shown to play an important role in the performance of the turbine. A trend of decreasing cycle-averaged efficiency at lower frequencies was measured. One of the principal objectives was to assess the degree to which the unsteady performance differs from the quasi-steady assumption. In order to make the steady-unsteady comparison for a multiple entry turbine, a wide set of steady equal and unequal admission flow conditions were tested. The steady state data was then interpolated as a function of three, non-dimensional parameters in order to allow a point-by-point comparison with the instantaneous unsteady operation. As an average, the quasi-steady assumption generally under-predicted the mass flow and efficiency loss through the turbine, albeit the differences were reduced as the frequency increased. Out-of-phase pulsations produced unsteady operating orbits that corresponded to a significant steady state, partial admission loss, and this was reflected as a drop in the quasi-steady efficiency. However, these differences between quasi-steady in-phase and out-of-phase predictions were not replicated in the measured results, suggesting that the unequal admission loss is not as significant in pulsating flow as it is in steady flow.

Unsteady Performance of a Double Entry Turbocharger Turbine With a Comparison to Steady Flow Conditions

Circumferentially divided, double entry turbocharger turbines are designed with a dividing wall parallel to the machine axis such that each entry feeds a separate 180 deg section of the nozzle circumference prior to entry into the rotor. This allows the exhaust pulses originating from the internal combustion exhaust to be preserved. Since the turbine is fed by two separate unsteady flows, the phase difference between the exhaust pulses entering the turbine rotor will produce a momentary imbalance in the flow conditions around the periphery of the turbine rotor. This research seeks to provide new insight into the impact of unsteadiness on turbine performance. The discrepancy between the pulsed flow behavior and that predicted by a typical steady flow performance map is a central issue considered in this work. In order to assess the performance deficit attributable to unequal admission, the steady flow conditions introduced in one inlet were varied with respect to the other. The results from these tests were then compared with unsteady, in-phase and out-of-phase pulsed flows most representative of the actual engine operating condition.

Investigation of Mechanical Loss Components and Heat Transfer in an Axial-Flux PM Machine

This paper investigates components of mechanical loss together with heat transfer effects in an axial-flux permanent-magnet motor. The mechanical loss components generated within electrical machines are well known; however, their prediction or derivation has not been widely reported in the literature. These, together with the electromagnetic loss sources and heat transfer effects, are crucial and must be accounted for when considering high-power-density, high-speed, and/or compact machine designs. This research is focused on separating the mechanical loss components to gain a more in-depth understanding of the effects and their importance. Both experimental and theoretical techniques have been employed in the analysis of a machine demonstrator. In particular, hardware tests with dummy rotors have been performed to measure the bearing and windage/drag loss components. These have been supplemented with computational fluid dynamics analysis to theoretically evaluate the aerodynamic effects occurring within the mechanical air gap accounting for loss and heat transfer. It has been identified that the analyzed hardware demonstrator suffered bearing loss significantly higher than that suggested by the bearing manufacturer. This has been attributed to design of the mechanical assembly accommodating bearings, which resulted in inappropriate bearing preload. The excessive bearing loss had a significant detrimental effect on the machine thermal behavior. In contrast, the aerodynamic effects have been found to have less pronounced effects here, due to fully enclosed and naturally cooled machine construction.

Comparison between the steady performance of double-entry and twin-entry turbocharger turbines

Most boosting systems in internal combustion engines utilize ‘pulse turbocharging’ to maximize the energy extraction by the turbine. An internal combustion engine with more than four cylinders has a significant overlap between the exhaust pulses which, unless isolated, can decrease the overall pulse energy and increase the engine pumping loss. Thus, it is advantageous to isolate a set of cylinders and introduce the exhaust gases into two or more turbine entries separately. There are two main types of multiple entry turbines depending on the method of flow division: the twin-entry and the double-entry turbine. In the twin-entry design, each inlet feeds the entire circumference of the rotor leading edge regardless of inlet conditions. In contrast, the double-entry design introduces the flow from each gas inlet into the rotor leading edge through two distinct sectors of the nozzle. This paper compares the performance of a twin and double-entry mixed flow turbine. The turbines were tested at Imperial College for a range of steady-state flow conditions under equal and unequal admission conditions. The performance of the turbines was then evaluated and compared to one another. Based on experimental data, a method to calculate the mass flow under unequal admission from the full admission maps was also developed and validated against the test results.Copyright

1-D Simulation Study of Divided Exhaust Period for a Highly Downsized Turbocharged SI Engine - Scavenge Valve Optimization

Fuel efficiency and torque performance are two major challenges for highly downsized turbocharged engines. However, the inherent characteristics of the turbocharged SI engine such as negative PMEP, knock sensitivity and poor transient performance significantly limit its maximum potential. Conventional ways of improving the problems above normally concentrate solely on the engine side or turbocharger side leaving the exhaust manifold in between ignored. This paper investigates this neglected area by highlighting a novel means of gas exchange process. Divided Exhaust Period (DEP) is an alternative way of accomplishing the gas exchange process in turbocharged engines. The DEP concept engine features two exhaust valves but with separated function. The blow-down valve acts like a traditional turbocharged exhaust valve to evacuate the first portion of the exhaust gas to the turbine. While the scavenge valve feeding the latter portion of the exhaust gas directly into the low resistant exhaust pipe behaves similarly to valves in a naturally aspirated engine. By combining the characteristics of both turbocharged and naturally aspirated engines, high backpressure between the turbine inlet and the exhaust port is maintained in the blowdown phase while significant reduction of the backpressure could be achieved in the latter displacement phase. This is directly beneficial for pumping work and residual gas scavenging. Combustion phasing & stability and turbocharger efficiency could also benefit from such concept. This simulation study was carried out using a validated 1D model of a highly downsized SI engine. Two degrees of freedom including the lift and the duration of the scavenge valve were optimized to achieve minimum BSFC. The potential for higher attainable BMEP was also briefly investigated at low engine speed.

Investigation of mechanical loss and heat transfer in an axial-flux PM machine

This paper investigates components of the mechanical loss together with heat transfer effects in an axial-flux PM motor. The mechanical loss components generated within electrical machines are well known, however, their prediction or derivation has not been widely reported in the literature. These, together with the electromagnetic loss sources and heat transfer effects are crucial and must be accounted for when considering high-power density, highspeed and/or compact machine design. This research is focused on separating the mechanical loss components to gain a more in depth understanding of the effects and their importance. Both experimental and theoretical techniques have been employed in the analysis. In particular, hardware tests with dummy rotors have been performed to measure the bearing and windage/drag loss components. These have been supplemented with CFD analysis to theoretically evaluate the aerodynamic effects occurring within the mechanical air-gap accounting for loss and heat transfer. Further to these, a 3D lumped parameter thermal model of the axial-flux PM demonstrator has been developed to validate predictions of the mechanical loss components and heat transfer mechanisms. The theoretical findings show good agreement with experimental data. Moreover, the research outcomes suggest that the mechanical and aerodynamic effects require careful consideration when a less conventional machine design is considered.

Extreme engine downsizing

This paper provides an introduction to the technical challenges and countermeasures required to enable extreme gasoline engine downsizing. Jaguar Land Rover (JLR) is the lead partner in a collaborative project called ‘ULTRABOOST’ which is supported with funding from the UK Technology Strategy Board (TSB). The project aim is to develop an innovative engine concept capable of a 35% CO 2 tailpipe reduction over the NEDC drive cycle relative to a current production V8 engine in a Sports Utility Vehicle, whilst maintaining key vehicle attributes such as performance and transient response. The project consortium is made up of eight technical partners including Jaguar Land Rover, Lotus Engineering, Shell Fuels, GE Precision Engineering, CD-adapco, University of Bath, University of Leeds and Imperial College London. Starting in September 2010 and running for three years the project will utilise the partners expertise and collective skills in engineering, design, combustion modelling, pressure charging and fuels to develop a highly pressure charged downsized engine concept. In this paper the technology required to enable extreme levels of engine downsizing and CO 2 reductions are described, together with accompanying simulation data collected from the initial concept engine development.

Off-Road Diesel Engine Transient Response Improvement by Electrically Assisted Turbocharging

Turbocharged diesel engines are widely used in off-road applications including construction and mining machinery, electric power generation systems, locomotives, marine, petroleum, industrial and agricultural equipment. Such applications contribute significantly to both local air pollution and CO2 emissions and are subject to increasingly stringent legislation. To improve fuel economy while meeting emissions limits, manufacturers are exploring engine downsizing by increasing engine boost levels. This allows an increase in IMEP without significantly increasing mechanical losses, which results in a higher overall efficiency. However, this can lead to poorer transient engine response primarily due to turbo-lag, which is a major penalty for engines subjected to fast varying loads. To recover transient response, the turbocharger can be electrically assisted by means of a high speed motor/generator. When the engine load is increased, the electrical machine acts as a motor to accelerate the turbocharger so that the torque demand can be met rapidly. Conversely, when boost delivery exceeds demand the electrical machine can act as a generator to recover energy that would otherwise be wastegated. This paper presents a model for the transient response of the electrically-assisted turbocharged engine when subjected to a step increase of torque demand. The base model is representative of a 7-litre turbocharged intercooled diesel engine and has been implemented in Matlab-Simulink and calibrated against test bed data. The model is used for the analysis of the dynamic behaviour of the engine with different levels of electric assist to the turbocharger. The results show that while turbocharger response improves with electric assist, compressor surge can occur in generating mode and that limitations on electric assist power are present.

SuperGen on ultraboost:variable-speed centrifugal supercharging as an enabling technology for extreme engine downsizing

The paper discusses investigations into improving the full-load and transient performance of the Ultraboost extreme downsizing engine by the application of the SuperGen variable-speed centrifugal supercharger. Since its output stage speed is decoupled from that of the crankshaft, SuperGen is potentially especially attractive in a compound pressure-charging system. Such systems typically comprise a turbocharger, which is used as the main charging device, compounded at lower charge mass flow rates by a supercharger used as a second boosting stage. Because of its variable drive ratio, SuperGen can be blended in and out continuously to provide seamless driveability, as opposed to the alternative of a clutched, single-drive-ratio positive-displacement device. In this respect its operation is very similar to that of an electrically-driven compressor, although it is voltage agnostic and can supply other hybrid functionality, too. In the work reported here a prototype SuperGen unit was tested on the Ultraboost extreme downsizing demonstrator engine and the performance compared to that of the originally-specified positive-displacement device. This engine has previously been described in detail and represents a 60% downsizing factor versus a 5.0 litre naturally-aspirated V8, although the ‘standard’ baseline combination of supercharger and turbocharger was found in earlier work to be a limitation on achieving the full downsizing factor at low engine speed. The improvement in full-load performance in the area where the turbocharger cannot generate the required boost by itself is reported. The transient response of the combined system at low engine speed is also presented, together with part-load fuel economy data at several engine speed and load points. Finally, this part-load data is used for vehicle modelling work showing that a more-efficient high-pressure stage can bring further fuel economy benefits to extremely-downsized vehicle applications.