up the pressure Building
Tony Lewin reports on the growing trend towards even higher line pressures in injection systems.
A
ll too often overlooked amid today’s rush to downsize, downspeed and turbocharge is the very process that gives
automobile engines their name – the combustion process itself. And central in that process, in modern engines at least, is fuel injection. It is the major influence on how the fuel burns, and thus how much power the engine produces and the composition of its exhaust emissions. Most of the significant quantum
jumps in engine performance over the past century can be traced back to innovations in the way the fuel or combustible mixture is delivered to the combustion chamber. First seen
on the exotic Mercedes 300SL in the 1950s, fuel injection brought the accurate metering of petrol in place of the more or less haphazard fuel admission provided by the carburettor. However, it was not until the 1980s and 1990s, with the widespread adoption of emissions limits and catalysts, that electronically controlled petrol injection became a near-universal fitment. The next move to direct injection
into the cylinder, is well underway in Europe, but is still at an earlier stage in other markets; again, the benefits in terms of efficiency and certain emissions are clear to see, and the synergies with lean burn combustion and turbocharging are powerful
enough to allow useful downsizing of the whole engine, with attendant benefits in parasitic loss reduction.
CRITICAL ROLE With the rise of petrol/gasoline direct injection (GDI) has come a new science: that of injector nozzle design. Irrespective of the pressures involved, the shaping of the nozzle and its holes plays a critical role in how the air/fuel mixture in the cylinder is distributed, and thus how the engine performs, in terms of start-up emissions, combustion stability and transient response. On the diesel side, ever since
Rudolf Diesel’s first prototypes ran around the turn of the 20th century, all diesel engines have required some form of pressurised fuel injection. Major steps along the way to
Diesel injectors for common rail from Bosch showing solenoid (left) and piezo actuation (right)
today’s prevalence of direct injection (DI) in the light vehicle segment have been the first passenger car DI from Fiat in the 1980s and the first common rail systems, again from Fiat, in the 1990s. The steady encroachment of electronic control, hand in hand with important developments in injector design – especially the piezo-electric nozzle – have brought dramatic increases in power and efficiency in the past decade, to the extent that diesels can now dominate endurance racing, as well as fly the flag for extreme economy in city cars.
20
www.automotivedesign.eu.com May/June 2013
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