Direct gasoline injection engines (GDI, FSI, TSI, TCe, EcoBoost) are now standard in modern cars. They provide good dynamics, lower fuel consumption, and meet strict emission standards. At the same time, they raise questions about the installation of LPG systems, and one of the key issues is gasoline injection.

What is it, why is it used, and does it affect the cost-effectiveness of LPG?

What is direct fuel injection?

In direct injection engines, fuel is fed directly into the combustion chamber rather than into the intake manifold. Injectors operate under very difficult conditions:

  • high temperature,
  • high pressure,
  • direct contact with combustion.

This design increases engine efficiency, but at the same time places high demands on the fuel system, especially with alternative fuels.

What is gasoline injection?

Petrol injection is a controlled, small amount of petrol supplied in parallel with LPG in direct injection engines. It is not an emergency or compromise solution, but rather part of the engine protection strategy resulting from its design.

Why is gasoline injection used in DI engines?

1. Stabilization of temperature and operating conditions of injectors

Gasoline injectors in DI engines are designed to work with gasoline and are located directly in the combustion chamber, supplying fuel at high pressure.
Gasoline:

  • absorbs some of the heat from the injector tip,
  • reduces thermal degradation,
  • stabilizes operating conditions,
  • reduces carbon deposits

LPG in its volatile phase does not perform this function, which is why the complete elimination of gasoline in many engines would lead to accelerated wear of the injectors. The gasoline injection therefore acts as a safety buffer in conditions where LPG alone might not provide optimal combustion parameters.

It is also worth noting that the durability of gasoline injectors depends not only on the fact that supplementary injection is used, but also on their design, manufacturer, and the engine in which they operate. Some types of injectors are more susceptible to seizing and carbon deposits, while others, with the same percentage of gasoline injection, are able to achieve significantly higher mileage without operational problems. Therefore, the strategy for controlling the LPG system should take into account the specific characteristics of the engine.

2. Engine protection under heavy load

During:

  • dynamic acceleration,
  • high-speed driving,
  • high thermal loads,

Gasoline enables:

  • more stable combustion,
  • better temperature control in the cylinder,
  • reduced risk of knocking.

3. Compliance with factory ECU strategy

Controlled gasoline injection:

  • allows compliance with factory control strategy,
  • reduces the risk of OBD errors,
  • facilitates maintaining appropriate fuel corrections

How much gasoline does the injection system consume?

Gasoline consumption with an LPG direct injection system is variable because it depends on:

  • engine design,
  • power and capacity,
  • driving style,
  • the gasoline controller strategy used.

Typical values:

  • 5–10% gasoline in less demanding units,
  • 10–20% gasoline in advanced units that monitor multiple parameters.

Despite the addition of gasoline, operating costs remain significantly lower than when running on gasoline alone.

Is it possible to drive on LPG without gasoline injection?

In theory, there are alternative technologies, such as liquid phase LPG injection through gasoline injectors. However, this system is practically no longer used and, due to numerous problems with engine operation, is no longer officially developed.

In practice:

  • they are not available for all engines,
  • they tend to be more complex and expensive,
  • they have limited compatibility and serviceability.

Therefore, in most popular direct injection engines, gasoline injection remains the safest and most predictable solution.

Does gasoline injection reduce the cost-effectiveness of LPG?

No. Despite partial gasoline consumption:

  • the cost per kilometer traveled is still significantly lower,
  • savings are noticeable even with moderate mileage,
  • the engine operates in safe conditions.

LPG systems designed specifically for DI engines, such as those developed by Autogas ALEX, take into account both the technical requirements of the engine and real operating conditions and OBD diagnostics.

An example is the ALEX IDEA system, whose special control algorithm provides additional protection for gasoline injectors across the entire engine load range. This solution is crucial for long-term operation of a vehicle on LPG, as it allows for precise adjustment of the injection strategy to the current operating conditions of the engine.

Summary

Petrol injection in direct injection engines is not a disadvantage of LPG systems or an unnecessary compromise. It is part of a conscious strategy to protect modern engines, resulting from their design and operating requirements.

A well-designed LPG system:

  • does not attempt to bypass factory safety features,
  • works with the ECU and OBD,
  • provides real savings while maintaining engine durability.