Fuel injection technology: extraordinary power for professional work

Fuel injection technology makes engines light and efficient – and turns a STIHL tool into a powerhouse that professionals can rely on.

A man wearing protective equipment working with a STIHL TS 500i cut-off machine on a construction site

A new league: power tools with fuel injection.

STIHL innovation harnesses the possibilities of fuel injection systems, creating powerful tools that need no carburettor.

What is fuel injection?

Fuel injection technology is a system for the introduction of a fuel-air mix to the cylinder of a combustion engine. In terms of the function it serves, it is an alternative to the carburettor, and has long been preferred in car engines. Understanding it better requires an overview of how an engine functions.

Oxygen: the key to engine performance

Achieving optimum engine performance is not so much a matter of the fuel you use as the air it is combined with. Much of the fuel circulating inside an engine is in itself simply a catalyst, required to help oxygen in the air react with hydrocarbon particles in the fuel. As such, the key requirement for fuel in an engine is that it is in the right place at the right time – as well as always in the right quantity. Only a perfectly proportioned air-fuel mix guarantees quick, complete combustion, and enables the engine to operate to its full potential. The key to designing high-performance, reliable engines is in ensuring this mix is right.

Carburettor vs. fuel injection

One way of providing the perfect air-fuel mix in an engine is via a carburettor. This is long-established technology, but far from straightforward; a carburettor is a mechanical component that mainly relies on the pressure differential between intake pressure and atmospheric pressure. The process usually runs smoothly, but there is a need to be aware of factors which could have a negative effect on the carburettor’s function: fluctuations in altitude and temperature; a contaminated air filter; engine wear; and fuel quality. That’s not ideal if you’re a professional power tool user and need to rely on performance at various altitudes and temperature conditions – which is why STIHL has developed tools with fuel injection systems. 

While a carburettor makes use of differences in pressure to mix fuel with air, fuel injection technology instead delivers fuel directly into the crankcase via an injection valve, or directly into the intake manifold – as is the case in the groundbreaking STIHL MS 500i chainsaw. The injection pump keeps the fuel pressure constant, thereby ensuring that the fuel injection valve provides exactly the right amount of fuel at any point during use.

Fuel injection system types

The principle of fuel injection is technologically brilliant, and there are a few different ways that fuel injection can be implemented. There are three main categories.

A man in protective clothing starting a STIHL MS 500i petrol chainsaw on the ground, in a deciduous forest.

The first chainsaw with electronic fuel injection: the STIHL MS 500i

The STIHL MS 500i chainsaw is the first mass-produced chainsaw in the world to feature electronically controlled fuel injection. This chainsaw offers unparalleled performance thanks to the sensor-controlled fuel injection system in the engine that self-adjusts to always provide optimum power. The technology offers countless benefits to tool users, and STIHL is breaking new ground in this area of innovation.

The innovative STIHL fuel injection system – as well as the associated elimination of the carburettor and carburettor components – means the power tools are exceptionally lightweight, and at 1.24 kg/kW have by far the best power-to-weight ratio on the market. High-capacity forestry professionals can depend on the STIHL chainsaw with fuel injection to offer noticeably more power than other models in the 80cm3 class, along with rapid acceleration and optimum start-up behaviour, whether from a cold or warm start.

STIHL has developed its own technology to provide the electronics in the tool with all the sensor data they need to control fuel injection. These electronics are operational right from start-up, even though the STIHL MS 500i has no battery and is started with a pull cord. In creating this engine STIHL has proved itself to be in the vanguard of professional petrol-powered chainsaw development, primarily on the basis of its electronic fuel injection technology.

Close-up of the manual fuel pump on a STIHL MS500i chainsaw being pressed

The truly innovative STIHL MS 500i fuel injection system

The fuel injection technology used in the STIHL MS 500i chainsaw injects fuel directly into the intake manifold via the injection valve, while an injection pump keeps the fuel pressure constant, thereby ensuring the valve provides the optimum quantity of fuel at any point during operation. The fuel quantity, injection point, and ignition point are automatically calculated by the STIHL MS 500i control unit – the crucial “brain” in the engine’s fuel injection system.

To optimise the fuel injection process, a number of sensors are installed in the powerhead crankcase. These include an external temperature sensor, a pressure sensor, and a temperature sensor to gather information on environmental conditions, which is passed to the chainsaw control unit. The sensors also record data that the control unit uses to calculate the intake air mass, making it possible to determine the perfect fuel injection quantity required for optimum combustion with greater accuracy than a carburettor ever could.

Another innovative technological detail in the fuel injection system is the generator, which produces power but is also used as a sensor. By means of the alternating current the generator produces, it provides information to the control unit about the speed of the machine and the position of the crankshaft – both essential to the fuel injection function. This enables the fuel injection control unit to very precisely recognise the chainsaw operating status and fuel requirement, and in doing so to adapt the fuel injection system and ignition to cope with any environmental conditions.

All of this happens in the space of milliseconds. This incredible technology ensures outstanding starting, optimal acceleration, and maximum performance throughout your working day. And there’s no need to think about cold starts, warm starts or any other manual settings on the chainsaw, as the electronics simply take care of it.

Advanced technology for stress-free work

Using a fuel injection system in a chainsaw engine makes light work of any job, as the engine has been comprehensively developed and designed for light weight with optimised displacement. The generator means that the conventional flywheel magnets are not required and the control unit is positioned directly on the flywheel. This design enables further efficiencies in cooling, which has made it possible to use a smaller flywheel than in conventional chainsaws of the same category; the extra flywheel mass required for idling is compactly provided by a steel ring below the fan blades, which not only supports the reduced flywheel size but also reduces the crankshaft load, further reducing overall chainsaw weight. The position in the tank housing of the injection control unit also offers optimum displacement, weight and centre of gravity – thereby additionally contributing to a compact and lightweight injection engine.

Summary: STIHL MS 500i chainsaw with fuel injection

  • The best power-to-weight ratio on the petrol chainsaw market: 1.24 kg/kW
  • Extraordinary acceleration: from idle to maximum engine speed in just 0.25 seconds
  • Optimum engine performance in all conditions
  • Unrivalled start-up behaviour in any weather and at any altitude
  • Straightforward start-up sequence without starter lever
  • Operation without manual adjustment