Until electric cars and other energy-efficient innovations are practical and affordable to all, the internal combustion engine will continue to be widely used, with the consequent greenhouse gas emissions. To help reduce pollution levels, EU-funded researchers have developed new laser ignition techniques, which have the potential to make combustion engines far more energy-efficient. 

Global concern about the negative environmental and health impact of greenhouse gas emissions has led to concerted action. The European Commission, for example, has set strict limits on emissions from industry and transport, and is investing in clean energy research.

Nevertheless, it is widely accepted that engines based on burning fossil fuels will continue to be used until alternative solutions (like electric cars, for example) are affordable at scale.

“Even when such alternatives are widely available, internal combustion engines will still be needed,” said LASIG-TWIN project co-ordinator Nicolaie Pavel from the National Institute for Laser, Plasma and Radiation Physics (INFLPR) in Romania.

Investigating laser ignition

The goal of the EU-funded LASIG-TWIN project was to investigate more efficient techniques for igniting fuels in internal combustion engines, like those you’d find in cars. Since the beginning of the 20th century, the electric spark plug has been used for ignition. The project team wanted to find out if alternative ignition systems, such as laser ignition, could make combustion engines more efficient.

“We wanted to better understand the benefits that laser ignition could bring,” said Pavel. “To achieve this, we created a network between the INFLPR (and its Laboratory of Solid-State Quantum Electronics in Romania) and four other highly renowned institutes from France, Germany and the United Kingdom. A key focus throughout has been on training and sharing learning experiences in the field of laser ignition.”

A range of techniques were investigated and trialled within the network. These included methods for packing and bonding optical and metallic materials to construct laser spark plugs. Visits to partner institutions were organised in order to share insights and carry out joint experiments.

“These visits were often followed by workshops, attended by universities, research institutes and private companies,” said Pavel. “In this way, we were able to increase the interest of industrial partners in laser ignition and achieve wider recognition.”

Two summer schools were held for students and young researchers in the field of laser ignition, with lessons given by experienced project researchers and university professors. International events such as the Laser Ignition Conference 2017, held in Bucharest, also helped to raise the project’s profile.

Energy-efficient combustion

Cross-country cooperation and training have led to the successful development of a prototype laser spark plug. The results were published in a widely downloaded paper in the journal Optical Engineering. In 2018, the innovation was trialled in a four-cylinder, multipoint fuel injection gasoline passenger car engine.

“The novelty of these tests was that the engine ran on lean air-gasoline mixtures (where there is a higher concentration of air to fuel than usual),” said Pavel. This means the fuel is less polluting. “We were also able to show that laser ignition of such lean air-fuel mixtures can actually lead to improved engine performance compared to electric spark plug ignition.”

The results could also lead to the development of a compact laser ignition system for stationary gas engines, of the type found in factories and power stations. This would result in efficient and energetic combustion with lower emissions. There are also hopes that laser ignition could be used in engines that run on ultra-lean mixtures of hydrogen and air at high pressure.

Pavel is confident that laser ignition will find its use in specific applications, such as propulsion systems for future space transportation, or in the operation of large natural gas reciprocating engines. At the same time, interest in this laser application depends on getting car manufacturers on board, willing to invest in the research and material resources needed.

“It should be noted that laser ignition systems will only become cheaper if they can be implemented on a large scale,” said Pavel. “Furthermore, additional tests are needed to ensure that these devices can compete with the simple and inexpensive electrical spark plug.”