###### Abstract  
Stringent emission regulations and increased demand for improved fuel economy have called for advanced turbo technologies in automotive engines. The use of turbochargers on smaller engines is one such concept, but they are limited by a time delay in reaching the required boost during transient operation. The amount of turbocharger lag plays a key role in the driver's perceived quality of a passenger vehicle's engine response. This paper investigates an alternative method to the conventional design of a turbocharger turbine to improve the transient response of a passenger vehicle. The investigation utilises the Ford Eco-Boost 1.6 L petrol engine, an established production engine, equipped with a turbocharger of similar performance to the GT1548 produced by Honeywell. The commercially available Ricardo WAVE was used to model the engine. Comparing the steady-state performance showed that the axial turbine provides higher efficiencies at all operating conditions of an engine. The transient case demonstrated an improved transient response at all operating conditions of the engine. The study concluded that, by designing a similar sized axial turbine, the mass moment of inertia can be reduced by 12.64% and transient response can be improved on average by 11.76%, with a maximum of 21.05% improvement. This study provides encouragement for the wider application of this turbine type to vehicles operating on dynamic driving cycles such as passenger vehicles, light commercial vehicles, and certain off-road applications. turbocharger; axial turbine; genetic algorithms; multidisciplinary design optimisation 2020 10 7452 22 October 2020 2020 22 July 2020 22 October 2020 22 October 2020  
the design of the turbine component of the turbocharger, used to recover energy in the exhaust gases to mechanical energy. Turbo lag is mostly apparent at low engine speeds, where the exhaust mass flow rate is not sufficient to provide enough energy to drive the turbine. Many methods have been suggested and tested to reduce turbo lag, but fundamentally, the most important is reducing the mass moment of inertia. An alternative method suggested by the Ford Motor Company (Dearborn, MI, USA) was the implementation of an axial inflow turbine to improve transient response [3]. Conventionally, turbocharger turbines employed in the automotive industry are radial inflow, whereby the exhaust gas enters the rotor radially and leaves axially. The axial turbine is different, in that the exhaust gases are axially guided by stationary guide vanes (stators) onto the rotor. Thus, the flow through the rotor is predominantly in axial and tangential directions and there is no radial change in the flow across the rotor. The benefit of this method over its conventional counterpart is that it typically, at the same diameter, provides a higher total-to-static efficiency and thus produces more power for the same flow conditions. This means that the axial rotor diameter can be reduced to produce the same power as its radial counterpart, thus reducing its mass and its inertia [4]. Even with lower inertia, like its radial counterpart, the axial turbine is still limited by turbo-lag, which is more evident at lower engine speeds and load conditions. Variable geometry turbine (VGT) technology is used to improve the performance of turbines at lower flow rates as well as higher flow rates by interacting with the flow to change the velocity and flow angles to achieve better turbine performance. The literature also reports the use of mixed flow turbines in turbocharger applications [5; 6]. The use of mixed flow turbines reduces inertia, and they also provide a flat efficiency characteristic, enhancing the performance at lower blade speed ratios. This paper however carries forward the analysis of an axial turbine concept carried out by [PERSON] et al. [7; 8]. The objective of this paper is to analyse the transient response of the turbocharger system using the axial turbine and to compare it with a conventional radial turbine.