Lean, mean, gas-burning machine

摘要

Engine builder Varity-Perkins has claimed that the Impco electronic mixture (gas:air) control system, used on its latest lean-burn liquefied natural gas (LNG) fuelled Eagle TXSi engine, achieves more efficient combustion and lower emissions than rival lean-burn gas engines. The patented system, developed in the US and incorporated on the LNG-fuelled Eagles specified by BOC Distribution Services for 10 32-tonne plated ERF tractor units, continuously "weighs" — separately — the quantity of gas and air going into the engine. This, says Perkins project engineer Brian McMurray, achieves a consistently optimised mixture strength. The system is more readily applicable to LNG than to CNG (compressed natural gas) because the gas liquefying process results in tighter control of fuel methane content. In CNG it is much more variable.