Challenging bus route on Mount Erciyes proves natural gas capability: Mount Erciyes is renowned in Turkey for high altitude winter sports, towering over the city of Kayseri located on the plains below. Connecting the ski resort with the city center and the villages along the way is bus route 4, operated by Temsa compressed natural gas (CNG) buses powered by Cummins L Series 8.9-litre engine. The clean, quiet running of the buses perfectly aligns with the pristine conditions on the mountain, where heavy snowfall takes the skiing & snowboarding into April, when the hiking season starts to take over in the Göreme National Park.

There are many reasons why this power solution is proving to be popular in Turkey, with one of the predominant factors being an abundance of natural gas supplied to the country and new pipelines coming on stream. At Cummins, we’re seeing more and more operators unlocking the potential of using gas technology in highly cost-effective bus operations. With the enhanced performance offered by the latest Euro VI Phase-D L9N natural gas engine, it looks as though that this market trend is likely to spread.

From city centre to mountain resort

The 19 mile (31 km) bus route from the city is a tough, continuous climb – with buses often loaded at full passenger capacity - but the L Series engine proves it’s strength every day by powering the buses up to an altitude of 7,250 ft (2,210 m) at the resort bus stop, passing the point where the thinner air (approximately a 5% reduction in effective oxygen compared to sea level) puts extra demands on the engine. As the bus fleet climbs and descends the mountain every day, moving across a wide ambient temperature range in the hour or so it takes to make the journey.

When down in the city, the Temsa buses share the roads with over 180 BMC buses also powered by Cummins natural gas engines. The growth of Cummins natural gas power in Turkey has been built on the high levels of uptime and reliability achieved whilst operating on routes with demanding duty cycles, as seen in locations such as Mount Erciyes and Kayseri. Cummins’ 8.3-litre natural gas engines has been operating in Kayseri, for more than 10 years, with the engine proving to be highly durable as well as providing clean and cost-efficient journeys operating in the densely populated historic city center. This success continues today with Cummins Euro VI Phase-D L9N engines powering hundreds of natural gas buses entering service in Turkey, as well as substantial bus exports to cities including Baku in Azerbaijan, in which operators can make the most of the locally produced natural gas.

Cummins natural gas engines offer a dependable, clean, and quiet performance, as well as low emissions, high efficiency, low total fuel costs, and reduced dependence on imported oil. But this is not to say that CNG is perfect for all uses as there are some significant infrastructure requirements compared to diesel. However, where gas supply is readily available, this offers a viable alternative.


To keep a 100 bus CNG fleet in operation running, a depot/station usually must be built with connection to a national gas grid. Many countries are subsidising this investment, as it is often not feasible to store compressed natural gas (CNG) on site, due to the tanks being much heavier and more expensive than diesel. One of the challenges to using CNG in countries that are naturally less resource rich is that storage tanks store 4-5 times less gas comparatively to the same volume of a diesel tank.

However, some companies offer CNG Mobile Refueling stations. The mobile refueling units can successfully transport up to 4,000 kg of biogas or CNG at 250 bar pressure to directly supply those vehicles. Each of these mobile gas stations can potentially fuel up to 40 buses or heavy vehicles, giving each vehicle a range of up to 400 kilometers.

Another option is liquefied natural gas (LNG) which is more like diesel in terms of its storage, but the tanks need to be cryogenically stored with an internal and external body of stainless steel to keep the temperature of LNG below 162 Celsius. One of the advantages of LNG is that you can transport the tanks in trucks and the difference in volume to traditional levels is not that significant. Some companies also offer mobile refueling units which can transport 25m3 of LNG and fuel up to 30 heavy vehicles.

Insight into alternatives

An alternative option to using CNG and LNG to power buses is renewable natural gas (RNG), also known as biogas or biomethane. This sustainable fuel option can contribute towards fleet decarbonization, either as a blend with, or as a 100 percent substitute for compressed natural gas. The latest generation of the Cummins L9N reduces NOx emissions by up to 80 percent below that of the Euro VI standard. PM emissions are also reduced, with testing revealing levels over 90 percent lower than the 0.01 g/kWh standard.

More recently, the L9N natural gas application range has been extended to include full size coach, revealed by Andadolu Isuzu in 2019 at the Busworld show in Brussels, offering the flexibility of intercity operations, tourist and student operation with a range of up to 700 km (435 miles). It is likely that natural gas solutions will receive more interest from manufacturers across Europe that are looking for low emissions solutions with a high sociability factor.

Evolving Technology

Technology will continue to evolve and advance to achieve the global aim of producing more efficient power solutions with lower emissions. But it is important to recognise that currently there is not a one-size-fits-all solution, and neither is there likely to be. Instead, it is probable that a mix of power options will be required in the near future, alongside continued innovation across diesel powertrain technology over the next decade.. Cummins is committed to bringing forward all the right technologies, from advanced diesel, clean natural gas and battery electric to fuel cell, at the right time. Cummins has over 100 years of power solutions heritage and we see this playing an important role in powering buses around the world for the foreseeable future.