[vasudeva]

Modern direct-injection diesel engines have a specific fuel consumption that is around 25% lower than comparable modern petrol engines. Because of the difference in energy density between petrol and diesel fuels, the advantage of diesel engines in joules is about 15%. The corresponding CO2 emissions are about 14% lower compared to a petrol engine. But diesels emit NOX which is causing smog and controversy.

The OECD has recently noted in `Cutting Transport CO2 Emissions’ that although diesel engines currently offer significantly better FE than petrol engines, but diesel has a higher CO2 intensity than petrol (ie more CO2 emitted per litre), so policies promoting diesel vehicles might not necessarily achieve any CO2 abatement. Approximate figures for kilogrammes of CO2 emitted per litre of fuel consumed with current engines are: diesel 2.6; petrol 2.4; sugar beet and grain ethanol 1.4; rapeseed/ biodiesel 1.3; sugar cane/ethanol 0.3. Although alternative fuels such as ethanol are less CO2 emitting, present prices of conventional diesel/petrol (inspite of recent price increases) have hampered investments in alternative fuels.

In Europe, new petrol vehicles sold in Europe from 2000 onwards (meeting Euro 3 or BS III in India) emit around 90% less CO, NOX and HC than vehicles sold in the 1980s, and emissions from new diesel vehicles have also been reduced significantly. This has contributed to reductions in local pollutants as newer vehicles with lower emissions have replaced older, more polluting vehicles. The vehicle emission standards were further tightened in 2005 with Euro 4. fter the introduction of these new standards, all new conventional petrol and diesel vehicles that meet these tighter standards will be extremely low emitters (and therefore ` near clean’) in terms of local air pollutants. The Euro 4 standards will achieve a 50% reduction in CO, HC and NOX emissions from new petrol vehicles, relative to Euro 3. For diesel vehicles, they will achieve a 50% reduction in NOX and PM emissions and a 20% reduction in CO emissions, relative to Euro 3.