Firing The Engine
Petrol engines get fired up with a spark plug. Diesel engines use direct fuel injection method in which the highly compressed hot air is used to ignite the fuel. During harsh winter, when the air isn't hot enough to ignite the engine (unlike petrol which gets ignited with a spark) diesel vehicles of the past have had starting trouble. But a new generation of diesel engines takes care of this problem.
Fuel Efficiency
Diesel gives more km per unit than petrol - because it has higher energy density and hence produces more energy per given unit. Diesel engines also use lesser fuel when idle as against petrol, by some account, just 1/3rd.
Example: Skoda Octavia (petrol) gives 8.1 km/l in the city as against the diesel which gives 10.7 km/l
Performance
Reaction to accelerator pedal, pickup for a petrol engine is faster and smoother. Diesel cars (without a turbo) have a slight lag in responding to the demand from the accelerator. But the latest CRDi engines with turbo chargers puts it neck-to-neck with petrol.
Example: Skoda Octavia (petrol) does 0-100 km in 9 seconds but the diesel takes 13.6 seconds
Power Factor
Diesel engines have a higher torque or turning power vis-a-vis the petrol ones. So when driving uphill on a lower gear, a diesel car will take lesser effort to drive up due to diesel's higher thermal efficiency and higher torque. This is the reason why heavy vehicles typically have diesel engines. But petrol engines give a far smoother, peppier ride
Example: Skoda Octavia (petrol 1.8) gives a maximum speed of 215 kmph as against diesel (1.9) that gives 175 kmph
Weight & Wear-Tear
Due to high compression ratios and high cylinder pressure, diesel engines must be built to withstand more wear and tear than petrol. As a result, critical car/engine components like crankshaft, cylinders have to be thicker and heavier. This makes them heavier and pushes up the sticker price.
Example: Octavia (diesel) gross vehicle weight is 1,855 kg as against petrol variant 1,810 kg
Better Mileage
Latest diesel engines are at least 25% more fuel efficient than petrol
Cheaper Commute
Diesel cars, though costlier, make sense if it clocks 11,000 km plus annually
Costlier Upkeep
Maintenance costs per km of diesel engine is 14% against 8% of petrol
Less Polluting
Cleaner fuel, latest tech and catalytic converters means diesel is no longer dirty
