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The present status and future developments of automotive outward compressing free piston gasifiers are discussed, with particular reference to gas generators in relation to turbocharged and compound engines, the present status of the machine produced by the authors' company, and the operating characteristics of a proposed 150 shaft horsepower gasifier-turbine-gearbox combination for vehicle traction. It is shown that under certain specified conditions, the gas generator cycle operates with superior efficiency, and with stated improvements in component efficiencies, the present gasifier will achieve a gas thermal efficiency of the order of 45%. Further, a vehicle power unit having an estimated specific weight of 8 lb/shp and volume of 9.75 shp/cu ft for the complete unit, with an overall torque ratio of 10:1, can be realized.

Turbine performance programs based on relatively simple one-dimensional considerations of great value when investigating the effect of variable nozzle angle or turbocharger matching, and compressor programs based on a combination of one-dimensional flow formulations for rotor and diffuser are discussed. A complete survey has been carried out and the results show that by use of optimized turbine nozzle angle and compressor prewhirl schedules, a fueling schedule appropriate to high torque backup at just over half engine speed can be employed without exceeding the operating limits of the engine with respect to air/fuel ratio (A/F), exhaust temperature, or maximum cylinder pressure.

Two systems involving an infinitely variable connection between engine and output shaft are investigated, viz: (a) the Differential Compound Engine (DCE) (b) the shunt-hydrostatic transmission coupled to a turbocharged Diesel engine. In both cases a given demanded input shaft condition can be met with a wide range of engine operating conditions. Since at least three external controls are available in both cases, viz: (a) fuel pump metering valve or governor set point (b) turbine nozzle angle (DCE) or hydrostatic motor swash (c) engine bypass (DCE) or hydrostatic pump swash optimisation of these control settings for best overall efficiency, torque backup or minimum emissions becomes a necessity and will form an important element in traction power plant design in the future.

The paper describes further work on the differential compound engine (DCE) which, following earlier theoretical work on the feasibility of multi-variable control is now being converted to microprocessor controlled continuous optimization for minimum fuel consumption for any demanded combination of output shaft conditions. The controlled variables on this integrated compounded engine transmission system include: i) engine governor set point ii) geared turbine nozzle angle iii) engine bypass setting and, additionally, in a system yet to be developed, but already theoretically investigated, fuel injection timing and duration. The paper describes the experimental and analytical procedures, using a programmable high response hydrostatic dynamometer, for establishing the 3-dimensional control surfaces for the above 3 variables, and the subsequent implementation of a microprocessor controlled system.

The paper describes the steps in the implementation of a self-optimising steady state micro-processor control system for the integrated truck engine transmission system known as the differential compound engine (DCE). References (1–5). Although the system in its present form is based on a small and slow microprocessor, the control strategy evolved is directly applicable to the faster system ultimately envisaged. The second part of the paper deals with the requirements for faster control of transients, with particular reference to operational safety requirements, such as limiting compressor speed and maximum cylinder pressure. It is considered that the unit forms the basis for advanced on- and off-highway vehicle power plant with uniquely attractive operating characteristics.

A differential compound engine is described which indicates it to be a significant advance over other traction prime movers. Its engine rating, as confirmed by both theoretical and experimental analysis, represents an increase of approximately 150% over the corresponding naturally aspirated engine. Furthermore, the compound mode of operation implies feedback of surplus power to the output shaft and therefore overall efficiencies in excess of engine efficiency, at least over part of the load range. Values of 40% in the neighborhood of the design point can be expected, experimental work having demonstrated engine brake thermal efficiencies in excess of 42-43%. Additional advantages include rising torque characteristics with decreasing output shaft speed, the incorporation of effective engine braking, and response characteristics superior to those of a turbocharged engine.

This paper introduces the development of a new idea in traction prime movers, to be known as the Differential Compound Engine. The DCE contains in addition to the compressor, an exhaust driven turbine geared into the output shaft, which leads to improved power and efficiency. It also enables the engine to operate at unchanged speed and power, regardless of output shaft speed. This concept was designed to provide an integrated engine transmission of high output and with stepless single pedal control.

The paper describes the results of a major development programme in association with industry on a prototype variable geometry turbocharger turbine coupled to a wide mass flow range compressor, and the matching of this unit to a standard Perkins T 6.354 engine. The performance target for the turbine was a mass flow turn down ratio of 2:1 and achievement of potential torque back up of 50% at half of rated engine speed. The results are described under the following headings: 1. TURBINE PERFORMANCE ASSESSMENT - Rig testing in high speed dynamometer for various settings of V.G. device and discussion of experimental results. 2. V.G. TURBOCHARGED ENGINE PERFORMANCE ASSESSMENT. 2.1 Steady state performance results. 2.2 Transient performance results. The paper concludes with a discussion of the potential of V.G. turbocharging in commercial applications.