Abstract
The increased stress on environmental protection and prices of crude oil from current reserves are the main reasons for the utilization of alternative fuels. Current contribution was carried out from the knowledge attainable from measurements on experimental, spark-ignition single-cylinder hydrogen-fueled engine at Technical University of Liberec.
The research of the combustion of very lean hydrogen & air mixtures on the testing single-cylinder engine in the laboratory of the combustion engines on the Technical University of Liberec has brought an important amount of information upon the properties of the combustion process of the hydrogen fuel. The paper describes the results from the experimental research work: by means of the thermodynamic analysis of the sets of indicator charts (150 cycles in each operating regime) and statistic processing of the data obtained from each set, a series of information on the course of the combustion of hydrogen & air mixtures in a piston engine has been obtained.
Hydrogen combustion makes it possible to achieve good NOx concentration levels required by expected long-term regulations if the combustion process is optimized carefully to utilize potentials and minimize harmful effects. Direct injection of hydrogen to a cylinder during inlet or compression strokes avoids backfiring typical for standard hydrogen engines and makes it possible to use high compression ratio, suitable for improved cycle efficiency. Optimum compression ratio, ignition timing, air excess ratio, fuel injection timing, boost pressure level and rate of exhaust-gas recirculation have been sought for using experiments and simulation calibrated by them to extrapolate trends. At the same time, the influence of exhaust gas contamination by lubricating oil and due to fuel impurities proceeding from fuel production have been also examined.
Hydrogen-air mixture can be easily burned in a SI engine in the form of extremely lean one the combustion stability being maintained very good. The very low NOX emissions from hydrogen-air mixture combustion are achieved at the air excess ratios of 2,2 - 2,5 (for idling even 3,5). Low-emission internal combustion engines for extremely lean hydrogen mixtures combustion should be supercharged (turbocharged) in order to obtain sufficiently high power density. Engine torque can be at least from one part controlled by boost pressure. Without any doubt, the hydrogen piston engine constitutes an alternative of the ecology-respecting drive of engine vehicles, and has evident prospects for the era of the after-crude oil age.
The present paper has been elaborated owing to the support of the grant GACR No. S 101/97/K053 Piston engine for the combustion of hydrogen driving unit of the future.