How does a diesel engine differ from a petrol engine?

When Rudolph Diesel created his first engine over a century ago, he could have had no inkling that his name would become one of the most instantly recognisable in mechanical history. In fact diesel engines have revolutionised heavy industry and now account for over 40% of new car sales in Europe. Although this is far from the case in Australia, there is no doubt that diesels are increasing in popularity. For many people the differences between a petrol engine and a diesel may not seem that obvious, but the two engine types represent a vastly different approach to internal combustion, and have very different attributes.

Diesel and petrol engines

Internal combustion engines work on the principle that a fuel is ignited and this releases energy. This energy is then contained and used to move the vehicles drive shaft, which in turn rotates the axles and the vehicle moves. But there are different ways of achieving this result and diesel approaches this issue differently.
Some of the main differences include:

• A petrol engine uses spark plugs to ignite the fuel
• A diesel engine uses compression as part of the engine cycle to ignite the fuel
• Diesel engines are much more thermally efficient, that is they release more energy from the fuel
• Diesel engines also do not rely upon intricate electronics for their ignition systems and are therefore able to operate in adverse conditions, such as the damp
• These sorts of engines also tend to be more durable than petrol engines, with a life span up to twice as long
• They also deliver more of their rated power out, more consistently, and have therefore often been used in heavy industry and agriculture
• Petrol engines work with a purely petrol fuel, whilst diesels use a fuel mixed with oil
• It is for this reason that diesel engines tend to be better lubricated and hence more long lasting
• Because diesels are more thermally efficient, they are also more fuel efficient – they get more energy out of the same amount of fuel
• Diesel engines actually produce less exhaust waste than petrol driven cars
• They have had a bad reputation for fumes due to connotations of industrial use, but today’s diesel engines have filters that remove much of the particle pollution
• The difference in cost to run is a combination of the different fuel efficiency and the cost of diesel relative to petrol
• Some diesel cars can make 1000 kilometres on a tank of fuel
• One thing that is off-putting to some motorists is that diesel can be ‘messier’ to use at the filling station and some people also don’t like its smell

Overall there are some important differences between the two engine types, and with fuel efficiency now being a big issue, diesels are coming into their own for commercial and domestic use.

Why choose a diesel powered car?

Diesels have a huge range of benefits and many of the negative associations such as plumes of black smoke belong far in the past. Today’s diesels have clean, efficient engines that provide excellent reliability and fuel efficiency. If you are thinking of buying  a car you would do well to consider diesel options.