Hydrogen as Homogeneous Charge Compression Ignition Engine Fuel

Abstract

Hydrogen has been proposed as a possible fuel for automotive applications. This paper reports an experimental investigation of hydrogen as HCCI engine fuel. The aim of the experimental study is to investigate the possibility to run an HCCI engine on an extremely fast burning fuel such as hydrogen as well as to study the efficiency, the combustion phasing and the formation of emissions. The experiments were conducted on a single-cylinder research engine with a displacement volume of 1.6 litres and pancake combustion chamber geometry. Variation of lambda, engine speed, compression ratio and intake temperature were parts of the experimental setting. The engine was operated in Homogenous Charge Compression Ignition (HCCI) mode and as comparison also in Spark Ignition (Sl) mode. Hydrogen was found to be a possible fuel for an HCCI engine. The heat release rate was extremely high and the interval of possible start of combustion crank angles was found to be narrow. The high rate of heat release limited the operating range to lean (λ>3) conditions. On the other hand operation on extremely lean mixtures (X=6) was found possible. The possible operating range was investigated when intake gas temperature was used for control and also this control interval was found to be narrow, especially when richer cases were run. The maximum load in HCCI mode was an IMEPn of 3.5 bar which is about half of the load possible in Sl mode and about half the maximum load in HCCI mode with other fuels. For the loads where HCCI operation could be conducted indicated thermal efficiency for HCCI was superior to that of SI. NOx emissions were, as expected, found to decrease when lambda was increased and the levels were very low in HCCI mode. High levels of hydrogen were found in the exhaust with HCCI. When the engine was operated on low lambdas (i.e. λ=3) emissions of carbon monoxide and hydrocarbons were detected, probably originating from evaporated and partially oxidized lubrication oil.