Analytical efficiency comparison between gas turbine and gas turbine hybrid engines for passenger cars

Abstract

The performance and emissions of two alternative types of gas turbine engine for a chosen family vehicle are compared. One engine is a regenerative 71 kW gas turbine; the other is a hybrid power plant composed of a 15 kW gas turbine and a 7 MJ flywheel. These engines would give generally similar vehicle performance to that produced by 71 kW spark ignition and compression ignition engines. (The turbine engines would be lighter and, with a free power turbine, would have a more favourable torque-speed curve (1), giving them some advantages.) Results predict that for long-distance trips the hybrid engine would have a considerably better fuel economy and would produce lower emissions than the piston engines, and that the ‘straight’ gas turbine would be even better. For shorter commuting trips the hybrid would be able to run entirely from energy acquired and stored from house electricity, and it could therefore be the preferred choice for automobiles used primarily for urban driving when environmental factors are taken into account. However, the degradation of remaining energy in flywheel batteries and thermal energy in the regenerator and other engine hot parts between use periods will result in more energy being used than for the straight gas turbine engine using normal liquid fuel. The higher initial cost and greater complexity of the hybrid engine will be additional disadvantages.