How load affects the performance of your engine

The rate at which load is applied by a machine affects the subjective and objective performance of the diesel engine powering the machine. With successful engine load acceptance, the engine will respond to the changing load demands as quickly as the machine it powers, giving optimum performance and continuous productivity.

Off-highway diesel engines are set to run at a speed which is maintained by the governor, regardless of the varying load applied by the machine. Applying a load slowly at a given speed does not lead to a significant speed reduction. However, if you apply the load quickly, some engine speed reduction will result. This transient, time-varying machine load can create a challenge known as ‘engine load acceptance’.

Extreme speed reductions may lead to your engine continuing to run below target speed, often known as bogging down, or in extreme cases, stalling. A small reduction in engine speed may lead you to the subjective view that your machine is not powerful enough. Large reductions in speed will objectively reduce your productivity.

Load acceptance
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Load acceptance

The rate of load application depends on the machine type and performance characteristics. For instance, hydraulic systems utilising the latest generation of swash pump have been developed for excavators and can lead to very high rates of transient load application. In these machines, load acceptance and engine speed control is a development challenge.

Development challenge

Traditionally, naturally aspirated engines do not generally suffer from load acceptance problems.  However, the advent of turbo engines for high power density has introduced a development challenge. 

Fuel systems are able to change fuel delivery more than 10 times faster than a turbocharger can significantly change air flow. Fuel and air need to be aligned to control the creation of smoke (Particulate Matter (PM)) so the rate of increase of fuel delivery may need to be controlled to the responsiveness of the turbo air system. In full authority electronic engines, strategies need to be included within the engine control system and subsequently the maps need to be populated based on development calibration.

Successful engine load acceptance means the engine is more responsive than the demands of the specific machine load application. This requires an understanding of machine systems and machine system development that might influence load application. It means developing control strategies and focused calibration to ensure the engine can follow the load application from the machine over its range of operating cycles.

Efficient particulate filters

The highest emissions standards are leading to wallflow diesel particulate filters (DPF) with very high levels of efficiency. With a DPF, it is possible to increase the rate of fuel delivery to improve load acceptance. However, fuel delivery still needs to be controlled to enable transparent management of the soot load in the DPF under the greatest range of machine use.

The proof of successful engine design and calibration is its ability to maintain engine speed within limits, thus supporting the objective and subjective productivity of your machine.

 

Cold start

Starting and reaching its operating speed is the primary functional objective of an engine. The operator depends on the engine’s ability to start and restart in a reasonable time in all conditions.

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Cold start

Speed control

In off-highway machines, the operator makes a speed demand and then loads up the engine through the operation of the machine. The engine has a ’speed governor’ that maintains engine speed under this varying load.

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Speed control

Mechanical or electronic

In highest regulated territories, electronic engine control is required to achieve the emissions standard. However, electronic engine speed control is available for lesser regulated engines and provides a number of benefits.

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Mechanical or electronic

Load acceptance

The ability of an engine to accept load and maintain engine speed is a function of both the engine and the machine. Maintaining speed under load affects productivity and leads to a perception of the capability of the machine and engine power.

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Load acceptance

Torque backup

When a machine overloads the engine at a target speed, torque backup will help to maintain engine speed and machine operation and recover engine speed when the overload is removed.

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Torque backup

Automated speed controls

When an engine runs at any speed under no applied load, we say the engine is at idle, or idling.  While idling, an engine burns fuel, makes noise and wears. Automated speed control strategies are designed to reduce idling time.

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Automated speed controls