Radical new engine for Honda Jazz

onda's New Jazz, which made its debut at the Frankfurt Motor Show in September and also wowed showgoers at Tokyo last month, is packed with technical innovation, including a revolutionary new powertrain. The engines form the second wave of the new generation of i-series units, which already includes the 200bhp, 2.0-litre i-VTEC fitted to the Civic Type-R.

Called i-DSI (dual and sequential ignition), the powerplant comes in both 1.2 and 1.4-litre versions and uses a radical new twin-spark ignition system with just two valves per cylinder. It improves efficiency and power while reducing fuel consumption and emissions.

W hen fuel and air enters the cylinder of an engine through the inlet valve, designers concentrate on optimising the swirl of the mixture to ensure fuel is atomised thoroughly and evenly. But however well the combustion chamber has been designed, the amount of swirl varies depending on revs and throttle opening.

To overcome this, the i-DSI engine fires its two sparking plugs at different times to ensure the mixture burns thoroughly whatever the prevailing conditions. At lower engine speeds, the spark plug nearest the inlet valve is fired much earlier than usual while the plug nearest the exhaust valve is fired later than usual. At higher rpm, the sparks are fired simultaneously.

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New i-DSI engine uses twin spark to improve power and reduce fuel consumption

he benefit of controlling the timing of each plug individually is that it increases cylinder pressure as the fuel burns and also allows a high compression ratio of 10.8:1 without causing any engine knocking.

Honda claims that efficiency levels of the new engines are approaching those of a modern, direct-injection diesel. Both meet 2005 EU IV emissions standards, the 1.2-litre engine achieving 18.8kpl on the combined cycle and the 1.4 18.2kpl. Power is impressive, too: the 1.2 delivers 77bhp and 11.3kgm torque, and the 1.4 82bhp and 12.3kgm. The CO2 outputs are 126gm/km and 131gm/km.

The engines are robustly constructed with rigid blocks and several heavy-duty components to absorb the additional noise created by the high cylinder pressures. Even so, they weigh eight percent less than the 1.3-litre Logo engine and are shorter and narrower. Early cars have five-speed manual gearboxes, but a new semi-automatic seven-speed continuously variable transmission (CVT) is on the way.