How Do BMW Diesel Engines Work?

 

BMW Diesel Engines

 

Diesel engines are forms of internal combustion engines where fuel is ignited by the high temperature and pressure of a compressed gas containing oxygen. This differs from a gasoline internal combustion engine which utilizes a separate source of ignition such as a spark plug.

Petrol engines compress fuel and air at a ratio of between 8:1 and 12:1. A diesel engine is able to compress from 14:1 to as high as 25:1. BMW diesel engines compress at around 17:1 and this higher level of compression compared to a petrol engine results in greater efficiencies as well as greater levels of torque.

 

Advantages of Diesel Engines

 

Because of the higher compression, diesel engines are more efficient than the petrol engines of the same size and therefore use less fuel to expel the equivalent energy. An example of this is the much cooler temperature of the exhaust system on a diesel car as much less energy is lost in the compression process compared to a petrol engine. This results in a far greater range of fuel per tank (or less fuel used per kilometer travelled).

The additional torque generated by the engine allows for a lower revving engine with torque levels equivalent to a V8 petrol engine. In the case of the 4-cylinder diesel, it has torque levels equivalent to a 6-cylinder petrol engine.

The latest generation diesel engines are friendlier to the environment in that they produce less Carbon Dioxide (CO2) emissions, Hydrocarbons (HC) - raw fuel - and Carbon Monoxide (CO) - partially burnt fuel.

The diesel engine is also more heavily reinforced to handle the higher combustion pressures needed for ignition. This, coupled with lower engine speeds, makes the diesel engine more durable with a potentially longer life.

Disadvantages of Diesel Engines

Diesel engines are slightly heavier than the equivalent petrol engine with the same power output due to the level of engineering as mentioned above. This adds to weight at the front of the vehicle and can impact upon dynamism compared to the equivalent petrol engine equipped vehicle. However, as the technology in diesel engines progresses further, disadvantages such as the weight of the engine block and the level of refinement have generally being addressed. A superb example of this is the latest generation BMW 6-cylinder engine found in the 530d and the X3 3.0d (see below).

Diesel engines also attract a higher initial price due to greater production costs involved in the manufacture of high precision injectors.

BMW technology in 6-cylinder diesel engines

The latest 6-cylinder diesel engine from BMW recently made its Australian debut in the 530d and the X3 3.0d. This engine has the latest technology from BMW in the form of an aluminum crank case (previously cast iron) which offers weight savings of around 25kg. It also embraces cast iron cylinder liners which are used to ensure strength and durability. The overall weight saving contributes to improved handling with reduced weight over the front axle, an improved weight distribution over both axles and greater fuel efficiency through carrying less weight.

The latest technology from BMW also incorporates the third generation common rail with Piezo injectors generating a rail pressure of 1600 bar. This system achieves its efficiency by being able to optimize the diesel engine by injecting fuel up to 5 times per engine cycle. This leads to better fuel economy, emission management and noise control as it optimizes the fuel injected and is even more precise in pre and post injection.

The latest BMW 6-cylinder diesel engine also utilizes the latest turbocharger system which is more responsive due to its ability to compress more intake air at the same turbo charger rotation speed. This eliminates any turbo lag previously experienced in acceleration and it does this more accurately due to its electric operation versus vacuum control of previous generation turbocharger systems.