Ignition Source

Introduction

It is inevitable that DIDSA is going to need to burn something; hopefully some form of rocket propellant. To start the combustion process, an ignition source will be required. This exercise will explore different methods, their pros and cons, and recommend a preferred ignition source for future projects.

Safety Considerations

This exercise deals with high voltages, high temperatures and a real risk of fire. Care should be taken to reasonably mitigate all hazards. DIDSA cannot take responsibility for the safety of those who choose to imitate or adapt the steps shown here.

This project involves high voltage and ignition sources. Please read the DIDSA safety guidelines before attempting any similar work.

Ensure you understand and comply with any local regulations that may apply to projects of this nature. Some aspects described here may be restricted by law.

The igniter shown here is intended for small scale experiments, demonstrations, research and learning. It is not a finished product and is not suitable for direct integration into other projects without further safety and engineering work.

Objectives

Primary

• Develop a DIDSA tested source of ignition that:
  • Is reliable
  • Is low cost
  • Can be controlled electronically and remotely

Secondary

• Provide professional development to DIDSA personnel
• Add ignition source research to the DIDSA information repository

Research

Two ignition methods commonly encountered are the spark generated by striking flint with steel, and electrical arcing produced in a gap between two conductors. Flint and steel are commonly found in camping supplies and mechanically operated lighters with a rotating wheel. Arcing is found more commonly in electrical igniters in gas cookers and BBQs.

Flint and Steel

A flint based igniter does not require a power source, its components are simple and low cost. It could potentially be included in a design where it can be operated electronically. It involves striking flint, which would require moving parts liable to seize, dislodge, or wear.

Electrical Igniters

Electrical igniters come in two forms: piezoelectric and an electric spark igniter. Piezoelectric igniters are usually operated by compressing a spring. The energy stored in the spring is then released to fire an object into a piezoelectric crystal. The potential difference generated creates an arc across a gap between conductors.
Electric spark igniters use a flyback transformer to create an oscillating high voltage current on the secondary windings capable of generating a high frequency spark between two conductors.
The major benefit of a piezoelectric igniter is that it does not require a power supply. A flyback transformer circuit does require a power source but it is easier to adapt for remote activation by an electrical controller.
For this reason, further focus will be on the construction of a flyback transformer electrical spark igniter.

Equipment and Parts

• Arc igniter DIY kit from AliExpress (or similar)
  • At the time of writing about £1.40 on AliExpress, £4.45 eBay UK
  • Contains electronic components and a PCB
  • Requires soldering
• Soldering iron
• Power source
  • e.g. 18650 cell, USB supply

Circuit

The following was supplied with the kit and shows the circuit diagram to be assembled.

When SW1 is closed a small bias is applied to the base of Q1, current then flows through primary coil of T1, this induces a current in the feedback coil. This adds to the voltage applied to the base, increasing the current flow through the primary coil. This cycle continues until T1 is saturated at which point the magnetic field in the core collapses rapidly and a very high voltage is felt in the secondary winding which causes an arc across the load gap. This repeats until SW1 is opened.

Construction

The kit is supplied with all necessary components and a printed circuit board (PCB). The PCB has symbols on the board showing the location and orientation in which they should be soldered. This makes the kit easy to assemble with basic soldering skills and equipment.
See the pictures below of the components and the assembled kit.

Demonstration

The video below shows a demonstration of the arc igniter:

Conclusions

This exercise has achieved the following primary and secondary goals at DIDSA:

• An ignition source has been identified that is low cost, reliable and can be operated remotely and automatically using a microcontroller
• Professional development in:
  • Electronics assembly and soldering practice
  • Electronics theory and application

Further Studies

Following this exercise further studies are necessary to:

• Modify the circuit to replace the switch with a relay or solid state switch to allow remote operation.
• Add a microcontroller and a touch screen to allow its inclusion in more complex designs.

These are outside the scope of this preliminary exercise and will take place in later DIDSA projects.