Why are Diesel cars priced more than Petrol cars?

Diesel engines run on higher compression ratios.On around 15-16. While Petrol engines have relatively lower compression ratio.   Because of higher compression ratio, the components are required to be tough built.They have longer strokes, which means taller engines, longer con rod, and a bigger crank, all making the engine heavier.And expensive.   Moreover due to torque requirement, a turbo-charger also sometimes becomes must which adds to the cost of diesel engines.   Ever wondered why bikes don't run on diesel engines ? Pretty much because of same reasons. It tends to make bikes super heavy and infeasible.

This answer would probably get into the finest details. It is because Diesel engines generate higher torque figures compared to the petrol ones. And the reason it generates higher torque figures is due to the fact that it operates at high compression ratios. The reason it operates at high compression ratios is because unlike spark ignition in petrol engines, diesel engines operate on compression ignition which means that the temperature of the air inside the combustion chamber is made so high that it is sufficient to ignite diesel.So we are dealing with some serious high pressure  inside engine cylinders, and for this reason the pistons, connecting rods, cylinder blocks, cylinder head , intake and exhaust valves , crankshaft , camshaft , flywheel , etc all must be strong enough to bear this torque and pressure brunt.Then ,since diesel fuel is more viscous than petrol, it takes some serious effort in delivering the fuel to the fuel injectors from the fuel tank. And for this you would require a tough fuel pump which should be able to gulp in diesel from the tank and flush it out to the fuel lines and thereby to the injectors at high pressure. Why at high pressure? Because diesel has to be finely sprayed over, evenly into the cylinders, otherwise it would not burn completely. Also ,suppose you are on an uphill journey, then the fuel pump has got to do a lot more work now to supply it to the engine. So some heavy weight pump is required.Then there is  a different type of catalytic converter for diesel engines called the diesel oxidation catalyst than a typical Three way catalytic converter in petrol engines. Now the problem is, the diesel oxidation catalyst cannot reduce NOx into Oxygen and Nitrogen. This makes the environment caretakers angry, and in order to please them you got to deal with the harmful NOx, and so you got EGR which stands for Exhaust Gas Re-circulation system in your diesel car. Then you got these fancy fuel injectors. It is a necessity for diesels but not for petrols.Then when you change a diesel fuel filter, run out of fuel or disturb the fuel system, air is trapped into the fuel lines. This air acts as a lock preventing the normal supply of fuel into the cylinder. To combat this, manufacturers got to supply your diesel car with a 'hand priming pump' to pump fuel through the system and replace trapped air.Then the fuel rails. And they got to be heavy duty ones.Then you got to have a transmission, clutch, clutch plate that are heavy duty ones to handle high torque.Then any typical diesel would have a turbocharger( a type of supercharger) to assist the engine in churning out more torque and lower rpms. And now if you have a turbocharger then you got to have an intercooler which cools out the pressurized air coming from the turbo.And all of this is the reason diesel cars are costlier than their petrol counter parts.

Petrol engine have low Compression ratio ranging between 7-11 but in case of diesel engine the value of compression ratio is 2-3 folds and ranges between 17-25. Higher the value of compression ratio higher the vibration caused due to running engine,so ultimately you will have to use a heavy chassis for a diesel car whereas a moderate chassis will do for petrol one. hence increment in price second reason which can be taken into consideration is engine internal equipments. A petrol engine is simpler than diesel one. as petrol engine is Spark ignition therefore only spark plug is needed to ignite the fuel,but a diesel engine has a dedicated mechanism for injecting fuel into cylinder. For this diesel engine is equipped with a fuel pump and a injector nozzle,fuel pump is used to regulate the supply of fuel and check on the load carrying capacity of vehicle as fuel pump is blessed with a governor this dedicated system costs about Rs 5000-20000 per cylinder,mid range cars are normally 4 cylinders so this equipment adds up at least 40000 in normal cars and at least 70000 in cars using CRD-i technology. The third and final reason which i can think about is the material cost. Petrol engine are generally low weight so material cost is very low,diesel engines are heavy and needs more material as compared to petrol engines

Let me take an example of recently launched Maruti Suzuki Baleno.Baleno Diesel Base model 1.3 Sigma costs around Rs 7,33,706 on road in New Delhi, whereas its Petrol cousin 1.2 Sigma costs Rs 5,73,835 on road. A disparity of Rs 1,59,871 is whopping to make brains go dizzy and think why to pay so much extra amount ?. In most cases Diesel engines have more capacity than its petrol brethren making diesel engines bigger and heavier. But cost of metal shouldn't make such a big difference. Difference lies in its way of working. A Diesel engine works on compression ignition which means that a high pressure common rail (~2000 bar) along with injectors, injects diesel directly into heavily compressed air (17:1) and the fuel self ignite due to high temperature. So, the high operating temperature ensures that the diesel enjoys premium treatment when it comes to component quality.Secondly, a diesel engine will always be equipped with a turbocharger higher torque means heavier flywheel, stiffer drive-shaft and so on and on.Coming back to my cost calculations ! If i go by above numbers of declared fuel economy and price of Diesel and Petrol in Delhi, i will have to clock 3,85,000 km to break even the price difference. This means 6500 km per month for at least another 5 yrs. So if someone is not required to drive 200 kms daily then buying a Diesel car is not a good preposition. Lesser the delta between fuel price more the break even period. Worst is the burden on pollution ( http://www.usstaad.com/go-green/future-of-ob-nox-ious-diesel-cars/) and technologies to make it cleaner will shoot the price even higher.

From your question i'm assuming you are asking the question in an Indian context. Simply put, diesel cars cost more than petrol cars because they have more components fitted on them. A diesel engine requires the 2 stage fuel filtration (single stage for gasoline), a fuel pump which generates around 400 bar of pressure (compared to the 3- 4 bar required for a Gasoline engine), fuel rails which can sustain this pressure for long duration (100,o00 kms minimum),  fuel injectors which have to be assembled in an extremely clean environment due to their sensitivity to dust and dirt (gasoline injectors can be replaced on the open road if need be), glow plugs to assist cold starts, expensive exhaust and after treatment systems to meet the emission regulations which are getting stricter by the day. The engine itself needs to have stronger noise insulation because (let's face it) diesel engines are inherently more noisier than a comparable gasoline engine- so you have cylinder blocks/ cylinder heads which are heavier than gasoline engines. Due to the high torque produced by diesel engines, the clutch and flywheel are bigger than in a gasoline engine. The common rail technology used in diesel engines is patented and only a handful make it - Bosch, Delphi and Mitsubishi come to mind. So they are going to charge a premium for deploying it on your vehicle. Hope I've shed some light on the reality of the situation.