The modern diesel is still king when it comes to efficiency, according to Dr Bernd Bohr, member of Bosch's board of management, as future drivetrain technologies, such as fuel cell vehicles, may be another 20 years away from being a viable proposition.
His comments will be welcomed by fleet decision-makers who have invested more heavily in diesel over the past few years, as well as company car drivers who have made the switch to ensure lower tax liability.
Bohr said: 'Diesel's special strength is its CO2 emissions, directly linked to fuel consumption. When assessing the competitiveness of individual drive systems, it should be done 'well to wheel', and in this respect diesel has an economy advantage of about 30% over the traditional petrol engine.
'But the spark ignition engine still has its place: petrol direct injection, which reduces fuel consumption, is now under further development.
'In addition we expect great savings potential from 'engine downsizing', with smaller engines giving a greater output due to turbocharging. Currently, only one production petrol or diesel-engined vehicle, the Audi A2 1.2 TDI, exceeds 70mpg and this model is not on sale in the UK.
Bohr claims engines are set to become 30% smaller for the same performance capability. He puts the sum of fuel savings for all imminent improvements at a further 20% for the petrol engine, and about 15% for the diesel, and adds that even greater economy will be gained from hybrid concept vehicles using brake-energy recycling.
He said: 'Even though a fuel cell is extremely efficient, the provision of hydrogen for it is very complicated, and the overall degree of efficiency when considered 'well to wheel' is only slightly better than that of the current diesel engine. We estimate mass production of hydrogen drive will not start before 2020.'
Bohr concludes that the internal combustion engine will remain the dominating power source for passenger cars for quite some time, projecting market shares of more than 95% until 2015 and 85% up to 2025.
Third generation common rail
Starting with the diesel, the industry is very reliant on new-generation injection as a means of reducing particulate matter and oxides of nitrogen. To this end Bosch has revealed its third-generation (G3) common-rail injection, which went into production in May, and will first appear at the Frankfurt Motor Show next month, as five or six European manufacturers are in the race to be among the first to use it.
At the system's heart is the 'rapid-switch' injector, using piezo-electric technology. Dr Ulrich Dohle, president of diesel systems division, explains the new injectors don't use a magnetic coil to control the injection valve, but instead rapid-acting piezo crystals.
'The movement of the piezo package is transmitted entirely without friction allowing more precise dosing of injected fuel, offering a reduction in pollutants.'
Overall, Bosch says third generation common rail (CR3) can reduce engine emissions by up to 20%, and that noise is typically reduced. But it's 10% to 15% more expensive than the current technology.
Beyond this the diesel holds further development potential. Bosch says the next improvement to common rail is planned for 2006, offering injectors with variable injection geometry, and injection pressure of 2000 bar.
Diesel exhaust treatment
A number of larger diesel cars weighing between 1.6 and 1.8-tonnes can already be made Euro IV compliant without the need for exhaust after-treatment. But the heaviest passenger cars with 'luxury' engines will not meet the legislation without exhaust after-treatment.
As PSA announces its second-generation particulate filter, so Bosch reveals it is to start mass production of its all-metal particulate filters from late 2005, which should last for the life of the vehicle.
The filter takes soot and particulates out of the exhaust gases and, once its soot storage capacity has been reached, the filter has to be regenerated with very hot exhaust gases to burn off deposits.
To raise exhaust temperature, EDC alters air intake, fuel injection quantity and timing. Quick-acting 3G common rail is perfect for this injection flexibility.
BOSCH is also developing 'spray guided combustion', in which an injector sited centrally in the chamber roof sprays fuel in such a fine stream that the fuel-air mixture can be ignited immediately. With current DI the mixture flows along the cylinder wall and is carried by a stream of air.
As this can be done away with, the energy, and so the fuel required to generate mixture flow, is saved, while better heat insulation between burning mixture and cylinder wall heightens efficiency.
DI-Motronic with spray guided combustion can achieve a further 5% decrease in fuel consumption, but is unlikely to reach the market before 2006.
Pumpe duse ALTHOUGH Volkswagen is currently the only volume manufacturer using this form of diesel injection, so-called Pumpe Duse (PD) represents a sizeable market for Bosch. The share taken by common rail is set to rise short-term to 65%, and that of PD to 16%.
PD currently provides the highest injection pressure at 2,050 bar, giving very low particulate emissions. Now there's a further development known as Coaxial Variable Nozzle, which differs from the conventional PD injector in the number and arrangement of the injection apertures.
A magnetic valve controls two nozzle needles and opens up two rows of jet holes, the first of which has a low flow rate and delivers small quantities of fuel at the start of combustion, so giving a 'soft', quiet burn. And under partial load it improves mixture quality, reducing particulate matter and NOx by 25% to 40%. When the higher-flow apertures open, engine performance is enhanced without having to increase injection pressure.
While these are substantial reductions in toxic pollutants, no specific claims are yet being made for reductions in CO2.
Petrol engine developments
DI-Motronic direct injection for petrol engines has reduced fuel consumption by some 10%, but in the near future additional improvements will make engines cleaner still.
Most fascinating among these is the supplementary electric compressor, an intake-air pump which increases engine torque at low revs to get rid of the slump in pulling power that's almost inevitable with 'downsized' small-capacity turbocharged engines.
The supplementary compressor pumps the engine with air it otherwise wouldn't get, increasing low-speed engine torque by up to 50%, and enhancing driving flexibility. The system has been designed to run on a standard 12v electrical system.
Additionally, Bosch plans to add a cost-effective automatic 'start-stop' function to its injection system, to reduce fuel consumption in stop-and-go traffic by turning the engine off automatically when it isn't needed. The gentlest press of the accelerator starts the engine again, without the use of a starter motor.
This new function of the direct injection system can fire up a combustion engine simply by igniting the combustion mixture, so decreasing fuel consumption by 5%.
Dr Rolf Leonhard, vice-president of development, Gasoline Systems Division, admitted that on a very cold engine Directstart can't do the job alone, and so isn't a substitute for a starter motor, although the starter can be smaller and lighter.
Don't expect to see either Directstart or the supplementary electric compressor in use before 2006, as production of both is anticipated for end 2005.