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LPG and CNG: The affordable fuels whose potentials are being unlocked by a pioneering spark plug

The idea of halving car fuel costs, while reducing emissions sounds ambitious. Yet this can easily be achieved today, with fuel technologies that have been around for decades: LPG (liquefied petroleum gas) and CNG (compressed natural gas). The world’s leading spark plug specialist NGK SPARK PLUG explores these alternative fuel sources – and the unique plugs specifically developed to optimise them.


All about LPG and CNG

Both LPG and CNG are extremely versatile, cheap and sustainable fuels. LPG is a naturally occurring by--product of natural gas extraction or an automatic result of the oil refining process, consisting of either propane, butane or a mixture of the two. Known also as Autogas, Propane, Propane Autogas, GPL and GLP, LPG is the third most used motor fuel in the world. An estimated 23 million vehicles run on LPG globally; with particular popularity in Eastern Europe, Benelux and DACH region. At normal pressure and temperature, LPG exists as a gas. When it is put under pressure or cooled, however, it condenses into a liquid state, reducing to 1/250 of its original volume. This means that it is easy to transport high amounts of energy in small amounts of space.
CNG, on the other hand, is a direct product of the natural gas extraction process. Consisting mainly of methane, CNG has a comparatively high ignition temperature of around 700°C. Unlike LPG, CNG is a fuel that always exists in a gaseous state, meaning that it requires more storage space. More than 20 million vehicles are estimated to run on CNG globally.

Lower costs and emissions excellence

Changing to gas brings drivers many benefits, chief amongst these being economy. Due to government incentivisation, LPG and CNG vehicles receive government subsidies in many countries. LPG and CNG, moreover, provide real savings in terms of fuel costs.

Whilst prices vary between countries, the average cost of LPG is consistently far less expensive than petrol or diesel; in many cases, more than 50% cheaper. LPG drivers can on average expect to save up to 40% on fuel expenses annually. CNG is generally even cheaper than LPG, although it produces less than half the amount of energy than LPG does; resulting in LPG being more cost-effective in the long run.

There is also a very strong environmental case for switching to LPG or CNG, which are among the lowest of all fossil fuels in terms of emissions. CNG is the cleaner burning fuel of the two, producing a smaller amount of harmful gases. LPG, however, still brings many benefits. Studies, for instance, have shown that using LPG instead of petrol or diesel contributes to far less CO (carbon monoxide), CO2 (carbon dioxide) NOx (nitrogen oxides) and HC (hydrocarbon) emissions. LPG, for example, produces 68% less nitrogen oxides than petrol and 96% less than diesel, not to mention 120 times less particulate matter than diesel. In addition, LPG exhaust fumes contain practically no black carbon, which is a major contributor to global warming as well as a serious health hazard.

Converting to gas

Although LPG vehicles are available from OEMs, it is more common for them to be converted. This requires having a second fuel system fitted at a workshop. Depending on the country, converting a petrol engine to LPG can take up to seven days and cost between €1,000 - €3,000. A converted car, which often has its LPG tank fitted in the tyre well in the boot, always starts from cold on petrol; meaning some fuel is still needed in the petrol tank. When the engine heats up after about a kilometre, the car automatically switches to LPG. Longer periods of driving can be achieved without filling up because when the LPG tank empties, the car automatically switches back to petrol. Even hybrid cars can be converted to LPG, making them cheaper to run and even more environmentally friendly.

Converting a vehicle to CNG is more expensive. Due to the fuel’s gaseous state, a CNG tank usually takes up more space in the boot, where it is normally fitted. CNG vehicles, however, are more commonly available from OEMs. Like LPG vehicles, it is possible to switch to petrol in CNG vehicles. In addition, more modern OEM vehicles can start from cold on CNG, eliminating the need for petrol altogether.

LPG LaserLine: the tailor-made solution for gas engines

LPG and CNG, however, place extreme demands on ignition; making spark plug selection especially important. LPG LaserLine from NGK SPARK PLUG was the Aftermarket’s first spark plug range designed especially for gas-powered cars. It comprises eight, double precious metal references, with a European market coverage of around 95%. “These plugs are ideal for LPG, CNG and bi-fuel operations”, says Kai Wilschrei, Senior Manager Technical Services Aftermarket EMEA at NGK SPARK PLUG EUROPE. “Before we filled this gap, the only available spark plugs for gas-powered engines, were those used in, and more suited to, petrol engines. This caused certain drawbacks for gas engines.”

LPG LaserLine: State-of-the-art spark plug technology for gas engines

1. High performance electrodes: Patented, double precious metal electrodes do not erode in gas combustion conditions, extending performance.

2. Unburdening the ignition coils: Thin, 0.6mm iridium centre electrode works with a low ignition voltage, reducing stress on ignition coils. Flame also expands faster, aiding ignition.

3. Optimal thermal behaviour: Copper core inside the ground electrode dissipates more heat, regulating high gas combustion temperatures.

4. Pre-set electrode gap: 0.8mm gap between the electrodes avoids manual adjustment.

5. Protective heat shield: Unique chrome alloy coating shields the housing from corrosion, safeguarding plug lifespan.

One issue was the risk of ignition coil failure. Because the combustion of gas is more difficult to ionise than the combustion of petrol, a higher ignition voltage (increasing by up to 7,000 volts) is required for LPG and CNG engines. This can make conditions ripe for ignition coil failure, as well as premature wear. “LPG LaserLine plugs counteract this by featuring a centre electrode with an iridium tip and ground electrode with a platinum chip; allowing the centre electrode to be very thin,” confirms Wilschrei. “This concentrates the voltage to one point, so that the ignition spark skips at a lower voltage, ultimately reducing stress on the ignition coils.”

A further challenge rectified by LPG LaserLine is that of corrosion. During combustion in gas engines, aggressive acids form which can corrode the spark plug thread. This can make the plug hard to remove at the end of its lifetime, or damage the cylinder head. “LPG LaserLine spark plugs have a special coating to ensure optimum protection from acid corrosion, ensuring they can be easily removed even after 60,000 km,” reveals the expert.

In fact, 60,000 km is the recommended change interval of LPG LaserLine spark plugs. This is considerably longer than for standard plugs used in gas engines, which generally have to be replaced twice as early as they normally would be in a petrol engine. Their endurance is due to the two precious metal electrodes, which despite their small diameter, display barely any burn-off. “The range offers true long-term savings,” says Wilschrei. “Not only do gas drivers save money by having to buy new spark plugs less often, they also cut down on installation costs.”

Heat management is a further challenge. Most LPG and CNG vehicles have the ability, at the touch of a button, to switch between gas and petrol as their fuel source. The combustion temperature in gas engines, however, is higher than in petrol ones. This means that the spark plug must be able to dissipate more heat, which is why LPG LaserLine spark plugs have an adjusted heat range. “Simply increasing the heat value risks the spark plugs sooting when the engine is running on petrol, because, dependant on driving conditions, they may be unable to reach the self-cleaning temperature,” warns Wilschrei. “To prevent this, LPG LaserLine plugs have an extended temperature operating range, which allows them to function optimally with both gas and petrol without overheating or sooting.”

Kai Wilschrei is proud of the advanced technology. “At NGK SPARK PLUG, we have an answer to all LPG and CNG special needs. Our plugs for gas-powered vehicles have a very high Aftermarket coverage, fitting almost 100 million vehicles in Europe. No matter the niche, we are passionate about developing the optimum ignition technology to fit the needs of every vehicle.” With over 80 years’ experience and a vast product portfolio, which includes spark plugs, glow plugs, ignition coils and leads, as well as a wide range of sensors, it’s no surprise that NGK SPARK PLUG is the trusted choice of distributors, workshops and drivers around the world.



Worldwide: NGK SPARK PLUG is one of the leading automotive and technical ceramics suppliers, with its corporate headquarters in Nagoya, Japan and sales organisations and production facilities all over the world. The automotive side of the company specialises in the fields of ignition and sensor technology, supplying Original Equipment and Aftermarket customers across the globe. Its product portfolio for the Aftermarket comprises spark plugs, glow plugs, ignition coils and leads under the NGK Ignition Parts brand, whilst oxygen and temperature sensors, NOx sensors, mass air flow (MAF) and manifold absolute pressure (MAP) sensors operate under the brand NTK Vehicle Electronics. With more than 14,500 employees, the company’s automotive and technical ceramics activities generate a total annual turnover of around 3.1 billion Euros worldwide. NGK SPARK PLUG’s European sales (including its EU, UK, France and Eurasia subsidiaries) account for 26% of this global turnover. NGK SPARK PLUG is represented on all continents and has 41 group companies, 24 production plants and five technical centres.

Aftermarket EMEA: NGK SPARK PLUG has seen significant growth across the Aftermarket since expanding beyond motorcycle parts into the automotive sector in the 1970s. With an outstanding commitment to quality, technology and research & development the company has become the world’s number one in spark plugs and oxygen sensors, and a leading provider of glow plugs, ignition coils and leads as well as further sensor technology. Organisationally NGK SPARK PLUG’s regional headquarters in Ratingen, Germany serves the Aftermarket across Europe, the Middle East and Africa. In the EMEA region the company has ten group companies and approximately 1,000 employees, as well as two production plants in France and South Africa and a technical centre in Germany.

For more information please visit:

For further information please contact:

Nicole Rößler, Senior Manager MarCom, Aftermarket EMEA, NGK SPARK PLUG EUROPE GmbH
Harkortstr. 41, 40880 Ratingen, Germany, AG Duesseldorf HRB 43118
Tel: +49 (0)21 02 974 102 E-mail:

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