Loaders without safety features?

Hello!

'I have noticed that several older truck models have turbochargers without pressure limiting devices (i.e., without wastegates, VTG, or VST). In a stationary application, this wouldn't be illogical, as you would select the turbocharger that is best suited for the specified operating range, and within that range, no pressure limiting is needed. This is because, given a specific fuel injection rate, the exhaust gas volume flow is also determined, and the boost pressure adjusts accordingly.'

What about those specific trucks, then? The maximum boost pressure should actually only be reached at maximum fuel injection and at the engine's rated power RPM. However, this behavior is impractical for a vehicle engine, because you would then need a transmission with an infinite number of gears in order to utilize the rated power.

While trucks from this era typically have around 10 gears, such an engine would be completely unsuitable because it would further restrict the already narrow operating speed range.

Did I misunderstand something, or are these engines actually designed in a way that makes them disadvantageous?

Best regards, Nebelwerfer.

'I have noticed that several older truck models have turbochargers without pressure limiting devices (i.e., without wastegates, VTG, or VST). In a stationary application, this would not be illogical, as you would select the turbocharger that is best suited for the specified operating range, and within that range, no pressure limiting is needed. This is because, given a specific fuel injection rate, the exhaust gas volume flow is also determined, and the boost pressure adjusts accordingly.'


WG, VTG, and VST are not used for limiting boost pressure!!!

Fixed-geometry turbochargers are not only used in older engines. Many modern commercial vehicle engines still utilize fixed-geometry turbochargers. Especially in larger-displacement engines, variable geometry turbochargers are simply not durable enough, partly because they are often also used for braking.

Commercial vehicle (CV) engines are consistently optimized for low fuel consumption. This is facilitated by low engine speeds at high loads. Therefore, a CV engine exhibits a much smaller range of operating speeds compared to a passenger car engine. Consequently, one can already speak of a near-stationary operating mode (cruising speed). Non-stationary operation plays a less significant role in CVs.


What about those specific trucks, then? The maximum boost pressure should actually only be reached at maximum fuel injection and at the engine's rated power RPM. However, this behavior is impractical for a vehicle engine, because you would then need a transmission with an infinite number of gears in order to utilize the rated power.


In a gasoline engine for passenger cars, this is likely an unusable behavior. However, in a commercial vehicle engine with a narrow operating speed range and a larger number of gears, it may not be a disadvantage.

However, the future will reveal whether the stricter emission limits and the resulting higher AGR (Agricultural Grant Rate) can still be reliably achieved with a fixed-bed reactor across the entire operating range.

Quote:

WG, VTG, and VST are not used for limiting charging pressure!!!

Why doesn't VW know that?

The N75 valve, which controls the WG (wastegate) and VTG (variable turbine geometry), is referred to in VW terminology as the "regulating valve for boost pressure limitation."

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I am not aware of any NFZ engines used in road trucks (i.e., up to 600 horsepower) that do not have a VTG turbocharger or a WG turbocharger.

vanilla299 zielte vielleicht auf das schlechtere Masse-Leistungs-Verhältnis bzw. auf die geringere Literleistung dieser LKW-Motoren ab. Man verzichtet absichtlich auf das Herausholen der theoretisch möglichen P max, indem man das nutzbare Drehzahlband nicht so weit ausreizt wie beim PKW-Diesel. Dadurch braucht der Starrlader nicht mehr für einen so hohen Luftdurchsatz ausgelegt werden, wodurch Betriebspunkte mit schädlichen Drucküberhöhungen weit geringer ausfallen. GrünThey can be.
-Focus on long shelf life.
- Avoidance of operating points with particularly low efficiency.
- Due to the high payload-to-unladen weight ratio, which is a consequence of the design, the engine's power-to-weight ratio becomes less critical. In fact, a certain minimum weight may even be desirable for the weight distribution of the towing vehicle.

@Nebelwerfer: This doesn't necessarily mean it's unusable. If a TDI engine were limited to 2800 RPM and had a fixed-geometry turbocharger optimized for that speed (with the same torque curve as the stock engine up to that point), it could still be usable for everyday driving, just like people already do when driving consciously economically. And the fixed-geometry turbocharger would need to be designed for 1/3 less airflow.

As far as I know, there are no NFZ engines used in road trucks (i.e., up to 600 horsepower) that do not have a VTG turbocharger or a WG turbocharger.

In the engine class commonly used for long-distance travel (approximately 12 liters / V6), turbochargers without a wastegate are definitely used. In my opinion, the proportion of engines with variable geometry turbochargers (VTG) is rather low in the larger V6 and V8 engines, simply because VTGs are not very durable. Of course, the proportion of VTG engines increases again in engines with smaller displacement.

As the name suggests, a wastegate always negatively affects the turbine's efficiency. In the commercial vehicle sector, a wastegate never has the same function as it does in a passenger car engine. Fuel consumption is always the priority, while responsiveness is less important.

Thanks for your replies. While many older truck turbochargers have a turbocharger, but lack turbo boost enrichment (like Steyr trucks), I assume that the turbocharger in those cases is primarily intended to ensure sufficient cylinder filling in the higher RPM range.

Consumption is always the priority; responsiveness is less important.

However, it's somewhat contradictory, as the efficiency decreases significantly at higher speeds, especially in NKW engines, simply because the frictional power must be considered per revolution, not taking into account the combustion speed of the mixture.


WG, VTG, and VST are not used for limiting charging pressure!!!


In most cases, yes, because a small, early-spooling turbocharger needs to be limited at higher RPMs to prevent it from over-boosting. This is especially relevant when considering a wastegate...



Positive displacement superchargers are not only used on older engines. Many modern commercial vehicle engines still utilize positive displacement superchargers.

Yes, for example, with emergency power systems, it's clear that the charging pressure of the engine load (fuel injection amount) follows and adjusts accordingly. The speed is predetermined by the synchronous generator to maintain the frequency. But what about when a truck needs to move uphill on a winding road? That would mean that the driver can't keep up with the shifting (unless they have an automatic transmission) to keep the engine 'happy' .

vanilla299 wrote:

As the name suggests, a wastegate always negatively affects the turbine efficiency. In the commercial vehicle sector, a wastegate never has the same function as it does in a passenger car engine. Fuel consumption is always the priority, while responsiveness is less important.

It's not necessarily true that optimal fuel consumption requires maximum power output. If improved torque at mid-range RPMs during driving is more beneficial, then a limitation might actually make sense. Furthermore, durability, at least in the case of the wastegate, is not necessarily a concern.

Thank you for your answers. While many older truck turbochargers have a turbocharger, but no charge air cooler (like Steyr trucks), I assume that the turbocharger only serves to ensure sufficient cylinder filling in the higher RPM range.

'Modern long-distance diesel engines without a turbocharger or variable geometry turbocharger achieve their maximum torque at 1000 rpm, while their rated power is reached at 1800 rpm. These relatively low speeds, compared to a passenger car engine (gasoline engine!), combined with the higher gear ratios in trucks, clearly indicate that a turbocharger or variable geometry turbocharger is not necessarily required in this application.'

However, it's somewhat of a contradiction, as the efficiency decreases significantly at higher speeds (especially in NKW engines), mainly because the frictional power must be considered per revolution, not taking into account the combustion speed of the mixture.

Since the frictional power increases with the speed in every engine, the maximum engine speed in (large-displacement) commercial vehicle engines is also rarely higher than 2000 rpm. This is mainly because fuel consumption is the priority.

In most cases, yes, because a small, early-responding turbocharger needs to be limited at higher RPMs, otherwise it will over-rev. Specifically, regarding wastegates....

However, there's a difference between a boost pressure limit and a turbocharger speed limit. If the turbocharger speed exceeds its limit, the boost pressure doesn't necessarily have to increase. To increase torque in the mid-range and improve responsiveness in a car engine with a turbocharger equipped with a wastegate (WG), the turbine needs to be bypassed, as you mentioned. Otherwise, the turbocharger speed will increase too much, and fuel consumption at high power levels will also increase significantly (high p3). The disadvantages are the 'wasted' exhaust energy when the wastegate is open and the lower efficiency of the smaller turbine wheel. Especially in gasoline engines with a large range of turbine flow rates (engine speed range), these disadvantages are accepted in order to achieve an engine with good responsiveness and high torque at low RPMs. This approach doesn't work in truck engines; the fuel consumption would be too high.


But surely, the optimal fuel consumption doesn't necessarily have to be achieved at maximum power. If improved acceleration at medium engine speeds during driving is more beneficial, then a limitation might make sense. Durability, at least in the case of the wastegate, is not an issue.

A turbocharger always reduces fuel efficiency at high power/load levels (due to wasted exhaust energy and a lower turbine efficiency due to the smaller turbine wheel). Since most long-haul vehicle engines are frequently operated at high power/load levels (the design point), the increased fuel consumption simply cannot be afforded in those situations.

Take a closer look at the power and torque curve of a larger commercial vehicle engine. The maximum torque is already achieved at 1000 1/min. When you examine the engine programs of many OEMs, you'll also notice the many different power variants available with the same displacement. If someone needs 250 kW, they won't buy a 350 kW engine. Besides the purchase price, this is mainly a question of operating costs (fuel consumption).

Most modern diesel engine turbochargers have a wastegate, but there are still some manufacturers who choose not to include one.