Diesel-like and HCCI-like operation of a truck engine converted to hydrogen

In addition to the traditional spark ignition (SI), premixed, gasoline-like and compression ignition (CI), diffusion, Diesel-like operation of internal combustion engines, premixed, homogeneous charge, compression ignition (HCCI) operation has also been proposed to improve the fuel conversion efficiency and reduce the pollutant formation. To be attractive, the operation in HCCI mode has to be coupled with the other traditional operations, being HCCI in general difficult to be controlled and limited to values of the air-to-fuel equivalence ratio λ within a narrow windows set by the lean burn limits with large λ and the peak pressure limits with small λ. Furthermore, the specific kinetics of hydrogen makes this fuel more difficult than other hydrocarbons to work in an engine operating HCCI without assistance. In a recent paper, the design of a 12.8 L in-line six cylinder turbo charged directly injected heavy duty truck Diesel engine fuelled with hydrogen has been discussed. Conversion of a latest Diesel engine with a novel power turbine has been studied replacing the in-cylinder Diesel injector and glow plug with a hydrogen injector and a jet ignition pre-chamber. The pre-chamber is a small volume accommodating another hydrogen injector and a glow plug being connected to the in-cylinder through calibrated orifices. This design permits to operate the engine in four different modes:–diffusion with jet ignition M1 - an injection occurs in the jet ignition pre-chamber before the main chamber fuel is injected and the engine operates therefore Diesel-like;–mixed diffusion/premixed Diesel/gasoline like M2 - an injection occurs in the jet ignition pre-chamber after only part of the main chamber fuel is injected and mixed with air;–premixed with jet ignition M3 - an injection occurs in the jet ignition pre-chamber after the main chamber fuel is injected and mixed with air and the engine operates gasoline-like;–premixed without jet ignition M4 - no injection occurs in the jet ignition pre-chamber and the engine operates HCCI-like.While only the Diesel-like operation was previously considered full load, all the modes including the operation HCCI-like are considered here over the full range of loads where the power turbine is either connected to the crankshaft or disconnected and the exhaust gases pass through this turbine or bypass the turbine.This paper deals with computational rather than experimental work. Computations are made with the latest predictive HCCI model using detailed kinetics of GT-POWER and the well established correlative Wiebe models for Diesel and gasoline combustion. HCCI-like operation is considered over a range of air-to-fuel equivalence ratio λ much wider than usually considered with other fuels being perhaps even more suitable than hydrogen to this operation thanks to the jet ignition assistance.

► Diesel-like operation permits better fuel efficiencies with hydrogen than Diesel.
► HCCI-like operation further increases the fuel efficiencies with hydrogen.
► Mixed Diesel/gasoline-like modes may permit intermediate results.