IVECO'S LOW EMISSION ENGINE
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• lveco's latest CNC engine, the 8469.21, is a charge-cooled 9.5-litre design which has full-loop stoichiometric control and electronic multi-point, sequential gas injection. CNC is delivered from the injectors at 7.0bar at precisely the right time, and as they are located in the inlet manifold, right next to the single inlet valves, the gas is quickly drawn into the combustion chamber. It was thought at first that two injectors would be needed per cylinder in order to supply sufficient gas in the required time, but the latest Bosch injectors have proved totally satisfactory.
For an indication of the transient potential of this engine. Iveco tested it against an earlier single-point-injection version of the same engine, and a standard Euro-1 diesel based on the same block and head. The engines were first tested in a Brussels bus, and then on an engine dynamometer in Turin.
The two types of test are not directly comparable: the road route is effectively a continuous transient test measured in g/km, while the 13-mode bench test is a series of steady-state readings weighted to reflect real situations and measured in g/kWh. They serve to show how much better the gas engine performs regardless of the test and in particular how well it can cope with transient, stop/start city conditions.
On the test bed, the engine running on CNG recorded a NOx reading that was just 5% that of the diesel; and on the road it reduced NOx to 2% of the diesel level. RC and CO emissions were also reducedagain, particularly in the "real" transient test (see table, below).
From Euro-3 onwards advanced gas engines will have to be homologated using the new European Transient Cycle (ETC), and although test conditions have been set, the actual pollutant limits are not yet.
And because ETC bears no resemblance to the existing [CE R49 13-made test, a correction factor will
be applied for comparisons. Regardless of how the test limits
are defined, hydrogen-rich natural gas, running in a dedicated SI engine, is set to produce excellent emissions results.
Even when natural gas is compressed to 200bar, the resulting CNG still needs five times as much tank capacity as diesel for a similar range. But this increase in capital cost is offset by a lower overall fuel cost. CNC has a higher energy content per kg than diesel. The less-efficient SI engine uses more fuel, but the duty on CNG is low, giving an overall fuel cost saving over diesel of around 13%.
lveco's stoichiometric engine is state of the art. It is a viable proposition which could make a major contribution to urban air quality, but it certainly isn't everyone's cup of tea.