Lista zgłoszonych artykułów

Spark ignition (SI) engines fuelled with compressed natural gas (CNG) are characterized by low levels of harmful exhaust emissions and a high knock resistance, but they suer from mediocre thermal eciencies. The relatively slow laminar burning velocity of methane, the main constituent in natural gas, is the underlying cause of a drawn out heat release duration when compared with gasoline. Consequently, advanced spark timing must be used to maintain mean-best-torque (MBT) characteristics, which results in higher pumping and heat transfer losses, as well as increased nitrogen-oxide (NOx) emissions. The method of fuel delivery (port vs. direct) is a further com- plication which results in a trade-o between reduced volumetric eciency and incomplete charge mixing. It is well known that higher levels of in-cylinder turbulence can increase the rates of combustion and mixing in engines. The diculty lies in producing adequately small-scale and high intensity turbulence at the correct time: immediately prior to and during combustion. One potential means of accomplishing this task is through the use of a split-cycle engine. The split-cycle engine divides the standard four stroke process amongst two separate cylinders: one for intake and compression, the second for expansion and exhaust. Fluid transfer between the cylinders occurs through a valved, high pressure passage and is timed so that the passage is approximately isobaric. Gaseous fuel is injected into this connecting passage at relatively high pressure (58 bar) and the subsequent air/fuel mixture is discharged into the combustion chamber under choked ow conditions. This is the primary means of turbulence generation and fuel/air mixing. This paper focuses on some preliminary experimental ndings of a small spark-ignited, split- cycle engine designed and constructed at the University of Windsor. Combustion characteristics for pure methane fuel at stoichiometric conditions are presented for low speed, mid-load operation. The fastest 10-90% mass-fraction-burn (MFB) durations are on the order of 6-7 °CA and relatively independent of engine speed. The challenges of achieving favourable combustion phasing within the physical operating constraints of the split-cycle architecture are discussed. High cyclic variation was also observed and hypothesized to the be the in uence of high-intensity turbulence on early fame development.