Analysis of a Modern Twin-Spool Supercharged Gas Turbine Engine Concept for Hybrid Vehicle Applications 2023-24-0127

This paper presents results from an extended analysis of a supercharged gas turbine concept initially proposed by Ford Motor Company in the 1960s. The concept was augmented through individual component improvements and utilization of new technologies developed over the 60 years since the inception of the original concept, known as the Ford “Type 704” engine. The model was constructed using Aspen Plus software and was validated in terms of the drive shaft power and brake-specific fuel consumption. The relative errors versus the data published by Ford were 0.06% in BSFC and 0.7% for shaft power and total fuel mass flow. The BTE matched the original Ford values to three decimal places. Having validated the model, a series of modernization steps were undertaken to bring the technology from six decades ago to a modern level. The model 704 has two spools, each connecting a compressor to its driven turbine with a separate power turbine positioned between the two other turbines. This configuration was modified by merging the low-pressure turbine with the power turbine and incorporating an electric machine on that spool for power take-off. Additionally, a second electric machine was added to the high-pressure spool, and the turbines were reconfigured to have an equal expansion ratio. The process resulted in a 64% relative improvement in BTE and a 39% reduction in BSFC while using the original turbine inlet temperature of 1200K. Recent improvements in material sciences suggest it is reasonable to go beyond this initial temperature limit, and therefore, a sensitivity analysis was carried out by varying the temperature up to 2000K. Furthermore, the effects of having different turbine inlet temperatures for the turbines after the two combustion chambers were investigated (in contrast to the Ford approach of maintaining the same inlet temperature for both turbines). By assuming a modern turbine inlet temperature of 1350K, the modernized Ford 704 has a BTE of 45.4% and a BSFC of 184.2 g/kWh. This represents an 87% improvement in BTE and a 47% reduction in BSFC in comparison to the data published by Ford. The result of the study has highlighted the capability of modern technology to simplify the complex Ford 704 engine model while improving efficiency and flexibility and perhaps demonstrating a route to a prime mover in a series hybrid application.