As answered by a fellow member in the earlier question, the factors which affect the performance as well as the emission of a diesel engine include:
- Optimization of the air flow (Both in quantity and in temperature)
- Proper injection timing
- Exhaust after treatment and recirculation
1) Air flow optimization deals with providing the engine with a greater amount of air to breathe. More air results in better combustion since oxygen is available in plenty. (This can be easily understood by imagining the case of a wooden piece burning with and without enough air. Lesser air causes the wood to burn with large amount of smoke. Same applies to the case of engines). Almost every diesel engine out there now comes with a proper air flow optimization. This may be achieved by proper placement of vents in the case of a regular family car whereas with turbochargers for high performance cars (Racing cars).
Even though general level of air input is sufficient for a regular diesel engine, for much larger ones, the amount of air supplied to them via the inlets may not be sufficient, especially when the engine is expected to deliver high power outputs. (Remember, diesel engines are not just available for vehicles, but for high power applications such as in generators and in factories for driving large systems)
The concept of obtaining a large power output is very simple. For a large power output, the amount of fuel burned must be large. In order to burn this large amount of fuel, you need more air inlet to the system. This is obtained by using a device called a turbocharger.The amount of cars using turbocharger is very less, except for some high performance or super cars like Lamborghini, Bugatti, Koenigsegg etc.(But they run on petrol)
Charge Air Temperature Management is a system provided in diesel engines to maintain the proper inlet air temperature. If temperatures are too high, it will lead to increased exhaust emissions. If temperatures are too low, starting the engine at low temperatures can be problematic and emissions during engine warm-up can become excessive. Various hardware are commonly used to achieve proper air temperature. In boosted engines, air coolers are used to keep air temperatures from becoming too high. Ensuring sufficient air temperature for cold starting can be achieved with glow plugs, electric grid heaters etc. In order to ensure proper working of the engine in varying situations, this system is provided in modern diesel cars.
2) Fuel Injection and its Timing: Diesel engines work by injecting fuel at a high pressure rather than using a spark plug to fire it up. (This is because of the fact that diesel as such is very difficult to be burned at ordinary pressures). The timing of injection is also very important here for proper working of the engine, since improper timing of injection will result in a large amount of unburnt fuel.
Now a day, the injection systems used in diesel engine is the Common Rail Injection System, which is supposed to be the best injection system available right now. The concept is rather simple: All the fuel injectors receive the fuel input from a common rail, with the injection controlled by the onboard electronics of the car.There are a number of different companies which use this system in their vehicles (Almost every diesel engine now has this feature) and each of them refer to these systems by their own names:
- Hyundai makes use of this system and calls it CRDi
- Honda calls it i-DTEC
- Jeep calls it CRD and so on.
It must be noted that despite their names, all of these things are the same.
3) Exhaust after treatment deals with the treatment of the exhaust from the engines so that the harmful substances are removed from the exhaust gas and only the cleaner part is exposed to the environment. As the name suggests, the system basically treats the exhaust from the engine so as to make it into the harmless form possible.The procedure in this system is the chemical treatment of the exhaust gases. The treatment system consist a tank of urea, which is used to treat the exhaust consisting of nitrous oxides and convert them into harmless nitrogen and water vapour.
Yet another system is the Exhaust Gas Recirculation. This involves recirculating some of the exhaust gas back into the intake system, and is an important technology that has allowed modern diesel engines to achieve very low engine emissions of harmful nitrous oxides.
In order to ensure proper functioning of an engine with EGR, various hardware, such as valves and coolers have to be introduced to control the flow, and the exhaust is introduced along with some inlet air. However here, the amount of air must always be maintained in such a way that there is enough oxygen for the engine to breathe.
Most of the modern diesel cars being released right now do have this mechanism.
The methods involved in the improvement of the exhaust quality of diesel engines include:
- The methods such as modification of chamber as well as cylinder designs to incorporate better air into the system and enable better burning are being tested now and are being slowly implemented.
- The greatest change in the design aspects of cylinder, piston and injector placements has occurred with military vehicles. This can be due to the extreme conditions where the vehicles have to perform and the load the vehicles have to carry. Examples include manufacturers like GHE-O.
- However, modern family car engines are also been found with slight changes in the designs so as to improve the efficiency and decrease the emission. Every company tests their cars with their own designs. The major change in the engines in ordinary family car has been brought by FIAT.
- However, luxury as well as supercar manufactures from Mercedes to Bugatti tests with their own patented designs for piston, cylinder and injector placements.
Apart from all these major systems, there exist a number of minor tweaks or systems in the engines which can affect the exhaust quality.
The on board electronic circuits such as the Engine Management System and Engine Control Unit has a great role in controlling the manner of the working of the engine and hence control the quality of the engine as well as the efficiency and the performance of the engine. It is these systems which control the engine pressures, timing of fuel injections.
The tweaks which affect the engine performance basically refer to the maintenance of the engine. No matter how good the engine is, without proper maintenance, (such as maintaining the required amount of engine oil) the engine will always work at a lower efficiency,decreasing the engine life, and causing large emissions.
Finally, as the answer to your question, Almost all these features are included in the Jeep Grand Cherokee, the Audi A3, RAM 1500 and the Mercedes Benz GLK. Engines which are being used in factories especially do have all these features to stick with the emission limits. However, the features like exhaust gas treatment are not available in every car around us.
However there is no point in expecting a diesel engine to produce zero emissions, even after all these mechanisms are adopted, there still exist a significant amount of emission (Which obviously is very much lower than the emission from an engine without these) from the engine. Let’s hope that the technological advancements in the future will find a way to tackle this problem.