Spark plugs: “generation gasoline direct injection”

Published: 30 July 2019

Bosch reports on the requirements of today’s vehicles

In modern spark plugs for gasoline direct injection engines, the centre electrode must be placed into the ignitable mixture.

Bosch spark plugs feature precise spark installation depth, projection and indexed ground electrodes for specific direct injection engines as required.

New engine concepts – a growing market

High performance and fuel efficiency are amongst the most important requirements placed on modern engines.

Driving vehicles combine comfort and fun whilst complying with current emission and consumption regulations.

As a result, the number of high-pressure supercharged gasoline direct injection engines is growing constantly – a growing market providing workshops with growing potential in terms of system maintenance and repairs.

As procedures and adjustment data have partially changed with modern systems, workshops depend on up-to-date information – even for the replacement of spark-plugs.

High demands of gasoline direct injection systems

In comparison with conventional naturally-aspirated engines, gasoline direct injection systems feature a number of advantages, including increased performance, reduced fuel consumption and pollutant emissions.

Due to the downsizing principle, the number and displacement of cylinders is reduced.

Turbochargers are thus used to achieve the desired performance.

The space inside the combustion chamber and the cylinder head is thus reduced accordingly. In the case of spray-guided gasoline direct injection, this results in a very small gap between the spark plugs and the injection valves – both of which are located between the intake and exhaust valves.

Due to aerodynamic effects, the fuel injected at a late phase of the compression stroke is quickly mixed with the surrounding air.

Orientation of the electrode towards the injection jet results in a very reliable ignition of the air/fuel mixture at any engine speed and load.

Bosch spark plugs for gasoline direct injection engines

In Bosch spark plugs for gasoline direct injection engines, the centre electrode is welded and aligned to be located right within the ignitable mixture once the spark plug has been installed.

Even minor impairments can quickly alter the spray pattern – with negative effects on the combustion behavioural.

As a result, spark plugs are to be produced with high precision: Once the ground electrode has been welded, the thread is rolled from an accurate specified starting point and with a precisely defined angle.

Even the design of the washer has been modified.

Compressible washers made of folded sheet steel, as those usually used for spark plugs, are designed for version with an install-ation depth of up to 0.25 mm.

In the case of gasoline direct injection engines, the installation depth is defined precisely.

Accordingly, the spark plugs for these engines are equipped with a solid, non-compressible washer.

Once the mechanic installs the new spark plug into the engine, it is placed at its precise position within the combustion chamber.

To ensure perfect fit, the torque values specified on the packaging must be observed in all circumstances.

A torque wrench must be used.

Torque-angle tightening is not enough anymore as it does not meet accuracy requirements, which results in over or under-torque and damage to the spark plug and/or engine.

Each engine needs its ‘own’ spark plugs

Bosch has been producing spark plugs since 1902.

This applies to both seriesproduction engines and motorsport applications.

To the present day, several motorsport teams equip their vehicles with Bosch spark plugs and injection systems.

Vehicle manufacturers around the world rely on Bosch know-how. Modern engines with smart gasoline direct injection need spark plugs perfectly geared to the specific requirements of each combustion chamber.

This is the only way to facilitate future optimisations in terms of performance, fuel economy and emission reduction.

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