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Ultra low exhaust emissions from Nissan gas truck

AT IMHX.NISSAN will be showing its latest DX Series ultra low emission gas truck on the Calor stand (No 07, adjacent Hall 17) at this year's IMHX. The forklift features Nissan's patented Tri-Cat System, which is fitted as standard. It reduces harmful exhaust emissions by up to 98 per cent and guarantees maximum fuel economy.

The system – a unique combination of three-way catalytic converter and computerised engine management technology – will be introduced across the complete range of Nissan LP gas trucks this year (2007) in an enhanced Tri-Cat Ultra version.

Soot-free exhaust has made LP gas an increasingly popular choice in recent years for operations involving inside working near to personnel, or where loads such as paper or textiles can be easily marked.

But as Nissan points out, unless properly controlled, the emissions from a gas-powered engine can be just as unpleasant – and harmful – as those from unclean diesel.

The Nissan TRI-CAT System is believed to be the only lift truck installation of its type with a catalyst which addresses all three of the toxic substances produced when LP gas is burnt. It reduces carbon monoxide by 91%, hydrocarbons by 96% and oxides of nitrogen by 98%.

A further feature of TRI-CAT is to provide optimum fuel economy through constant engine management. Electronic sensors continually monitor engine output, controlling and supplying just the right air-to- fuel ratio for the truck's operational requirements.

Regardless of the composition of the LPG fuel, environmental conditions and the condition of the engine, say Nissan, the TRI-CAT System always provides optimal combustion.

As well as ensuring minimum gas pollution and maximum fuel economy, the “closed loop” air fuel ratio control helps to minimise maintenance.

“Most manufacturers do not fit a catalytic converter at all as standard to their gas-powered trucks,” said Nissan's National Technical Manager, Doug Wyatt. “When some do, it is typically a low-cost two-way system. Most often this fails to address oxides of nitrogen (NOx), and is generally not as efficient as the Nissan system in removing hydrocarbons (HC) and carbon monoxide (CO).”

In addition to extremely low levels of toxic emissions, tests in a standard work cycle have shown that the TRI-CAT System can typically save 5,000 litres of LPG over a five year period.

This is due to the air-fuel ratio being calculated 1,000 times per second by an electronic controller receiving signals from engine management sensors within the truck.

The quality of oxygen in the exhaust is measured by a lambda sensor which detects if the combustion is optimum. Engine revolutions and water temperature are also monitored, with a vacuum switch cutting in to provide more fuel when greater power is required, and a throttle switch to reduce flow when the engine is idling.

The Nissan “closed loop” system for air-fuel control is believed to be the most advanced to be used in lift truck technology. With no need for adjustment, a controller calculates precisely the fuel quantity required. In contrast, conventional LPG control systems typically rely on the volume and vacuum of the air sucked in by the engine to decide the fuel quantity. The air-fuel ratio is set by mechanical adjustments during maintenance, with no provision for automatic correction due to component wear, less than ideal flow characteristics, or sudden changes in load demands.

With such systems, tuning deteriorates little by little, resulting in growing fuel consumption and increasing exhaust emissions until the truck is next serviced.

“Conversely,” concludes Doug Wyatt, “constant monitoring by the closed loop in Nissan's TRI-CAT System results in optimal combustion all of the time.” Nissan Forklift
Tel 0800 919968.
e: forklifts@nissan.co.uk
web: www.nissanforklift.co.uk

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