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Efficiency, torque, driving style

The Diesel engine has become popular among the currently running large commercial vehicle engines mainly due to its high torque, high performance and excellent efficiency.

However, the efficiency of our Miller cycle LPG engine reaches the efficiency of a diesel engine.

The driver is the pedal positionwith controls the charging of the engine. And the charge determines the torque for both Diesel and LPG engines. Half

gas pedal pressed = half torque,gas pedal pressed to the floor = maximum torque.

In the diagrams, the thick black line represents the maximum torque, the green field the most favorable efficiency.


The efficiency of the Diesel engine already reaches its most favorable efficiency at a speed of 1,100-1,400 rpm with the gas pedal half depressed. For such a favorable efficiency the LPG gas pedal is a you have to push it in much more than halfway. Note that the torque and speed ranges of the two engines are significantly different. The Diesel engine cannot be "revved" because the diesel will not have time to burn. And the LPG engine, which has a much smaller torque, achieves the highest performance at higher revolutions.


Therefore, the driving style of the two engines is different:

  • for diesel:

    • favorable efficiency is achieved even with the gas pedal barely half-pressed

    • the maximum efficiency is the gas pedal position approx. It's about 2/3 of the way through

    • when the gas pedal is fully depressed, the torque and power increase, but the efficiency decreases

  • For LPG:

    • the gas pedal approx. Press it down to 2/3 to achieve the favorable efficiency

    • and the maximum efficiency is at full depression, i.e. at floor gas

So, in the case of a diesel engine, preferably around 2/3, relatively

widebe in the pedal position range, on the contraryLPG

to at least 2/3pressing the gas pedal, but rather

let's drive on floor gas. These are the right speed

can be achieved by choosing degrees.

In the case of LPG, it is particularly important to switch to such a high gear when cruising speed is reached that the vehicle cannot accelerate even with low gas(there should be no torque reserve in this gear). E.g. in the case of MAN TGA85 km/h, 1,300 revolutions, top gear 8. At full load (40 tons) there is no torque reserve. But if we switch back - we want to accelerate, or an uphill is coming - then up to 2,500 rpmwe can let the engine down, so we can take advantage of the approx. 80% power reserve.

Diesel engines are better in this regard, because they have a power reserve of up to 200% due to their structure.

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