1930-1992 Car Nostalgia: Do You Remember the Indirect Injection?

1930-1992 Car Nostalgia: Do You Remember the Indirect Injection?


 – What is indirect injection?

 – Indirect injection: historical reminders

 – Indirect injection today

If you are a car enthusiast and nostalgic for indirect injection on earlier cars, you will like the explanations in this post on the disappearing technology of the indirect injection system.

 What is indirect injection?

 We might as well make it clear right away that new vehicles whether gasoline or diesel, are no longer equipped with this type of injection, condemned by the latest US and EU standards to control light-duty vehicle emissions.

 Definition of indirect gasoline injection

 It is the position of the injectors that determines the type of injection. For indirect gasoline injection, they are placed before the intake valve. Therefore, it is an air/fuel mixture that is admitted into the engine through the opening of the intake valve. The injectors open into the combustion chamber above the piston, the air alone is admitted through the intake valve. The mixture of the two components is made in the combustion chamber.

 The hydraulic part of this injection system consists of:

 – the fuel tank;

 – an electric fuel pump, usually immersed in the tank;

 – a fuel filter;

 – a fuel rail on which the electromagnetically controlled injectors are fixed.

 Note: the supply and injection pressure generated by the fuel pump varies between 2.7 and 3.2 bars.

 It contains for the electrical part:

 – an engine management computer that determines the injection time after processing the engine parameters;

 – sensors that transform the physical values of the parameters (air pressure, engine temperature, engine and camshaft speed, gas analysis, engine load, etc.) into variable electrical signals for the computer;

 – actuators, controlled by the ECU (injectors, ignition coil, relays, solenoid valves…).

 Definition of indirect diesel injection

 Contrary to indirect gasoline injection, the injector is placed after the intake valve, but it opens into a pre-chamber in communication with the combustion chamber. The air above the piston is compressed as the piston rises. At the end of the compression, the diesel fuel is injected into this chamber where pre-combustion takes place in contact with the superheated air (400°C). A chain reaction ensues and causes complete combustion in the main chamber.

 This type of injection avoids, among other things, too violent efforts on the piston. The system consists of a supply circuit and a high-pressure circuit.

 The supply circuit includes:

 – the fuel tank;

 – the diesel filter;

 – a rotary pump housing a vane transfer pump, which sucks the fuel from the tank (the supply circuit is therefore in negative pressure).

 The high-pressure circuit is composed of:

 – the same rotary pump, synchronized with the engine timing system, which generates the high pressure of 110 to 175 bars; exclusively mechanical distributor pump that serves each cylinder in the order of ignition;

 – the injectors, also exclusively mechanical; a calibrated spring determines their injection pressure.

 Indirect injection: historical reminders

 Let’s go back in time:

 – 1930: indirect injection dates back to the 1930s when Mercedes worked hard to develop both gasoline and diesel engines;

 – 1936: the first real implementations on mass-produced cars were the Kugelfisher mechanical indirect injection for gasoline on the Peugeot 404 and for indirect injection for diesel, Mercedes in 1936 and Peugeot in 1938;

 – 1960: Indirect diesel injection is introduced, while gasoline engines still operate mostly with a carburetor;

 – 1993: the generalization of the indirect gasoline injection; the new vehicles having this year the obligation to be equipped with a catalytic converter, associated with the injection for its operation;

 – 2002: gradually, US and EU programs to control light-duty vehicle emissions will condemn these two types of injection in gasoline and diesel, which produce too many polluting emissions.

Indirect injection today

Although new vehicles are no longer produced with indirect injection, many used cars are still equipped with it, and it still offers certain advantages:

– Maintenance: whether in gasoline or diesel, indirect injection is very reliable and proven, and repair interventions are few and well mastered by professionals. The engines, especially the atmospheric version (without turbo), are very reliable and accumulate miles.

– The financial aspect: due to their age and older technology, their purchase price is low, and they can be easily resold as a second car in the household, or even appreciated by those who are afraid of new technologies and the hassle of maintaining them in the electronic field.

However, this generation of vehicles is gradually disappearing, pushed by official incentives (scrappage scheme, “old diesel” taxation, etc.). Their defects are now clearly denounced:

– fuel consumption is higher than for the new generations (10 to 20% more);

– the vehicles are much less efficient than those with direct injection, especially for diesel;

– they pollute more, although the new models are not free of NOx (nitrogen oxides) and fine particles (they do not exist with indirect gasoline injection).

In short: the disappearance of these indirect injection vehicles, whether gasoline or diesel, is inevitable, as they have been overtaken by the ecological requirements for preserving the planet.

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