Laser Ignition for Internal Combustion Engines

1. Laser Ignition for Internal Combustion Engines Dean Clewis Nick DeMarco PHYS 43 – Modern Physics Dr. YounesAtaiiyan Semester Project SRJC

2. So, what is a ? Generally, most of us think of lasers like this, which isn’t entirely wrong…

3. What is a Laser? • A laser is a device that emits electromagnetic radiation through a process of optical amplification based on the stimulated emission of photons. • The term ‘laser’ is an acronym for Light Amplification by Stimulated Emission of Radiation • The emitted laser is unique in its high degree of spatial and temporal coherence. • Spatial Coherence means a fixed phase relationship between the electric fields at different locations across the beam. Typically it is expressed through the output being a narrow beam which is diffraction-limited, also known as a "pencil beam." Laser beams can be focused to very tiny spots, achieving a very high irradiance. • Temporal coherence means a strong correlation between the electric fields at one location, but different times. Electric field distribution around the focus of a Gaussian laser beam with perfect spatial and temporal coherence. A laser beam with high spatial coherence, but poor temporal coherence A laser beam with poor spatial coherence, but high temporal coherence.

4. How does a Laser work? Lasers are monochromatic, meaning they are very orderly forms of light that have only one wavelength and one direction.It all starts with the electrons. By sending energy to a system we can achieve what is known as population inversion. This means that there are more electrons in the excited states than those in the lower energy states. As one electron releases energy (a photon), the other electrons strangely seem to communicate with each other and also begin releasing photons. This chain reaction of releasing photons is called stimulated emission. The problem now is that these photons are released in random directions. In order to make sure this energy is all forced in the same direction, mirrors are strategically laced within a laser to direct the photons. The photons are directed by bouncing back and forth between the mirrors, hitting each other and causing more stimulated emission. So, by having:- Population Inversion- Stimulated Emission- Strategic Planting of MirrorsWe get:- Monochromatic , Directional, and Coherent light.

5. Types of Lasers • Gas • A Helium-Neon (HeNe) used mostly for holograms such as laser printing. • Chemical • Lasers that obtain their energy through chemical reactions. Used mostly for weaponry. • Dye • Uses organic dye as the lasting medium, usually in the form of a liquid solution. Used in medicine, astronomy, manufacturing, and more. • Solid-state • Uses a gain medium that is a solid (rather than a liquid medium as in dye or gas lasers). Used for weaponry • Semiconductor • Also known as laser diodes, a semiconductor laser is one where the active medium is a semiconductor similar to that found in a light-emitting diode. • Applications include telecommunication and medicine

6. Standard Spark Plug Ignition in an Internal Combustion Engine • Current internal combustion gasoline engines use spark plugs to ignite the air/fuel mixture in each cylinder (located at the top of the combustion chamber).

7. Laser Ignition System for an Internal Combustion Engine Laser ignition will replace the spark plug seen in current gasoline engines.

8. Laser Ignition System for an Internal Combustion Engine (continued) • Laser Testing: • A one-cylinder research engine was used as a test engine. • The research engine was equipped with a four-valve DOHC cylinder head with a spray-guided combustion system of AVL List GmbH. • Engine test runs were carried out with two different approaches: • First, a plane window was inserted into the cylinder head of the engine. A focusing lens was placed in front of that window in order to focus the laser beam down into the combustion bomb (“separated optics”). • Second, a more sophisticated window was deployed. A lens-like curvature was engraved directly into the window. By using such a special window, no further lens was required (“combined optics”). • From the point of view of components development, the main goal is the creation of a laser system which meets the engine-specific requirements. Basically, it is possible to ignite mixtures with different types of lasers.

9. How Laser Ignition Works • The laser ignition system has a laser transmitter with a fiber-optic cable powered by the car’s battery. It shoots the laser beam to a focusing lens that would consume a much smaller space than current spark plugs. The lenses focus the beams into an intense pinpoint of light, and when the fuel is injected into the engine, the laser is fired and produces enough energy (heat) to ignite the fuel. • Below is a diagram of the laser arrangement:

10. Why Laser Ignition? • Regulations on NOx emissions are pushing us toward leaner air/fuel ratios (higher ratio of air to fuel). • These leaner air/fuel ratios are harder to ignite and require higher ignition energies. Spark plugs can ignite leaner fuel mixtures, but only by increasing spark energy. Unfortunately, these high voltages erode spark plug electrodes so fast, the solution is not economical. By contrast, lasers, which ignite the air-fuel mixture with concentrated optical energy, have no electrodes and are not affected. • Natural gas is more difficult to ignite than gasoline due to the strong carbon to hydrogen bond energy. • Lasers are monochromatic, so it will be much easier to ignite natural gases and direct the laser beam to an optimal ignition location. • Because of the requirement for an increase in ignition energy, spark plug life will decrease for natural gas engines. • Laser spark plug ignition system will require less power than traditional spark plugs, therefore outlasting spark plugs. • Ignition sites for spark plugs are at a fixed location at the top of the combustion chamber that only allows for ignition of the air/fuel mixture closest to them. • Lasers can be focused and split into multiple beams to give multiple ignition points, which means it can give a far better chance of ignition.

11. Why Laser Ignition? (continued) • Lasers promise less pollution and greater fuel efficiency, but making small, powerful lasers has, until now, proven hard. To ignite combustion, a laser must focus light to approximately 100 gigawatts per square centimeter with short pulses of more than 10 millijoules each. • Japanese researchers working for Toyota have created a prototype laser that brings laser ignition much closer to reality. The laser is a small (9mm diameter, 11mm length) high powered laser made out of ceramics that produces bursts of pulses less than a nanosecond in duration. • The laser also produces more stable combustion so you need to put less fuel into the cylinder, therefore increasing efficiency. • Optical wire and laser setup is much smaller than the current spark plug model, allowing for different design opportunities. • Lasers can reflect back from inside the cylinders relaying information such as fuel type and level of ignition creating optimum performance. • Laser use will reduce erosion.

12. Future Research Needs and Shortcomings • Cost • Concept proven, but no commercial system yet available. • Stability of optical window • Beam Delivery/Laser induced optical damage • Particle Deposits • Intelligent control • Laser Distribution • Multiple pulse ignition • Multiple point ignition • Single Point Ignition: • Timing optimization (phasing) vs Thermal Efficiency • NOx tradeoffs • Knock margin • Multipoint Ignition: • Higher flame speed may provide additional knock margin as well as a higher burn rate. • Multipulse Ignition: • May provide improved ignition, leaner combustion, and lower emissions. • May provide a way to circumvent beam delivery issue.

13. Acknowledgements • http://www.laserist.org/Laserist/showbasics_laser.html • http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA427076 • http://www.maik.rssi.ru/full/lasphys/05/7/lasphys7_05p947full.pdf • http://www.carbontrust.co.uk/SiteCollectionDocuments/Grant%20Funded%20Projects/075,%20076,%20077%20projects/076-207%20University%20of%20Liverpool%20final%20PDF%20locked.pdf • http://www.laserist.org/Laserist/showbasics_laser.html • http://affleap.com/laser-ignition-system-to-replace-spark-plugs/