India, June 23 -- The biggest reason why Indians have preferred a diesel engine when purchasing a new vehicle has been the low running cost vis-a-vis a petrol car. Better mileage and lower per litre cost convinced most - especially those who drive long distances - that purchasing a diesel vehicle was the more economical decision regardless of other factors like impact on environment and high maintenance costs. But as fuel prices across India continue to soar, the difference in price of the two fuels is steadily reducing with the gap in Delhi almost negligible now....