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The paper presents reportage of the debate on the topic expressed by its title that was held as a special session at the SAE 2003 Congress, supplemented by commentaries on its highlights. The debate brought to focus the fact that fuel cells are, indeed, superb powerplants for automobiles, while hydrogen is at the pinnacle of superiority as the most refined fuel. The problems that remained unresolved, are: (1) when fuel cells will be practically viable to replace internal combustion engines and (2) under what circumstances hydrogen, as the ultimate fuel, will be economically viable in view of its intrinsically high cost and hazards engendered by its extraordinary flammability and explosive tendency.

The paper is based on the premise that the sole purpose of combustion in piston engines is to generate pressure for pushing the expansion process away from the compression process (both expressed in terms of appropriate polytropes) to create a work producing cycle. This essential process, referred to as the dynamic stage of combustion, is carved out of the cycle and its salient properties deduced from the measured pressure profile, as a solution of an inverse problem: deduction of information on an action from its outcome. An analytical technique, construed for this purpose, is first presented and, then, applied to a direct injection, spark-ignition, methanol fueled four-stroke engine.

The sole purpose of combustion in a piston engine is to generate pressure in order to push the piston and produce work. Pressure diagnostics provides means to deduce data on the execution of the exothermic process of combustion in an engine cylinder from a measured pressure profile. Its task is that of an inverse problem: evaluation of the mechanism of a system from its measured output. The dynamic properties of the closed system in a piston engine are expressed in terms of a dynamic stage - the transition between the processes of compression and expansion. All the phenomena taking place in its course were analyzed in the predecessor of this paper, SAE 2002-01-0998. Here, on one hand, its concept is restricted to the purely dynamic effects, while on the other, the transformation of system components, taking place in the course of the exothermic chemical reaction to raise pressure, are taken into account by the exothermic stage.

Significant improvement of engine performance can be achieved by ushering in a micro-electronic system to control the execution of combustion - an exothermic process whose sole purpose is to generate pressure. Hence, the primary feedback for the controller is provided by a pressure transducer. The activators are piezo-electrically activated pintle valves of MEMS type. The task of the micro-electronic processor is to provide an accurate feed-forward signal for the actuators on the basis of the information obtained from the feedback signal, within a time interval between consecutive cycles. Furnished here for this purpose is an algorithm for an interface module between the pressure sensor and the governor. Concomitantly, the gains thus attainable in the reduction of fuel consumption and curtailment of pollutant formation are thereby assessed. The implementation of this method of approach is illustrated by application to a HCCI engine.