Well to Wheel Emissions Simplified 


What are "well to wheel" emissions? We answer your questions about a topic that's on everyone's radar as the world continues its march to a zero emissions future. 

The first phases of greenhouse gas regulations for commercial vehicles focused on tailpipe emissions, and this perspective brought the industry many efficiency improvements. With the advent of low to zero carbon fuels and new power sources, like battery electric powertrains that get their energy from charging via the electric grid, differences in GHG emissions are more difficult to assess. 

What is well to wheel efficiency and emissions? 

Regulators targeting reductions in GHG emission realized that both the amount of fuel or energy source, and GHG emissions associated with the production, processing, distribution, and use of the fuel, needed to be quantified. This was the advent of well to wheel comparison. 

Well to wheel is the most complete and accurate way to evaluate efficiency and emissions, considering the entire energy consumption and all greenhouse gas emissions of the complete life cycle of an energy source.

Well-to-wheel vs tank-to-wheel emissions

While well to wheel emissions consider the GHG emissions generated during the entire lifecycle of a fuel, the term tank-to-wheel is a subset of well to wheel, referring to the use of a power source during operation only. These are the tailpipe emissions that were once the cornerstone of regulation and assessment but can no longer tell the whole emissions story.

For example, the bar chart shows tank to wheel and well to wheel annual GHG for the line-Haul truck application. From a tank to wheel perspective, the BEV powertrain has zero emissions, and would be considered better than most ICE options fueled by diesel. Running on a renewable biofuel shows no benefits with this measure. The lower bar of the hybrid configuration shows that efficiency improvements provide GHG emissions reductions, as well.

The comparison between the powertrain options looks different when compared on a well to wheel basis. Here, the important factor is that there are GHG emissions associated with producing, transporting and distributing, and using each of these fuels.

First, notice that the ICE bar is taller. This increased height accounts for petroleum extraction, transportation, refining and distribution. With these additional considerations, the BEV bars are now non-zero. For example, if ‘average electricity’ from across the US were used to power the truck, the GHG emissions from ICE with diesel is actually lower than BEV. If greener electricity from California were used, BEV shows reduced GHG emissions over a fossil fueled diesel engine but are still non-zero.

The benefits of running on a renewable fuel (Biofuel) are much clearer when considered on a well to wheel basis. In our example, biofuels provide the highest reduction in GHG emissions, but the height of the hybrid diesel bar is similar to that of BEV in California. This indicates that higher performance ICE-based powertrains can provide substantial GHG benefits.

Annual GHG Emissions
*Note that this is based on a real application (line haul), chosen to highlight the potential to miss viable ways to reduce GHG emissions. The relative heights of the bars will be different for other applications. 

Technologies to lower well-to-wheel emissions 

When it comes to lowering GHG, it’s not a matter of which technology is better — but rather which is more suitable to a specific set of conditions and needs. We have to consider range, weight, downtime, performance requirements, customer economics, and related infrastructure to provide the best options for the market. This is why a company like Cummins is working to develop and improve multiple technologies for myriad applications.

Advanced diesel engines provide significantly improved fuel economy and feature after-treatment systems, resulting in a reduction of GHG. You can find advanced-diesel engines in many applications ranging from line-haul and regional-haul trucking to construction and agriculture applications.

Fuel-agnostic engine platforms can offer customers the option to select the right fuel to get the job done with minimal to no output of GHG emissions for a specific situation.

Low- and zero-carbon fuels can be used as an alternative to traditional fossil fuels in many applications. These fuels show a marked reduction in GHG in many different sections of the well to wheel lifecycle. Renewable diesel, for example, merely returns carbon to the atmosphere—the same carbon atoms that the source plants used from the atmosphere. Some of these fuels, such as renewable natural gas (RNG), can even deliver sub-zero emissions.

New power technologies such as battery, fuel cell and hydrogen produce no carbon dioxide while in use, but well to wheel emissions help to show us the full picture of their best and most useful applications.

Beyond ‘well to wheel’: other lifecycle considerations 

Well to wheel emissions analysis gave manufacturers and regulators a more holistic view of the fuel lifecycle, but new technologies have brought further considerations even outside this purview.

Raw material extraction and battery production can result in significantly more GHG emissions than the production and use of internal combustion engines. Batteries that power electric vehicles will, eventually, reach the end of their life, and both recycling and “second life” options are being explored and refined.  

As technology becomes more and more advanced, these “cradle to grave” considerations may replace well to wheel as the driving force toward a zero emissions future.

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Catherine Morgenstern - Cummins Inc.

Catherine Morgenstern

Catherine Morgenstern is a Brand Journalist for Cummins, covering topics such as alternative propulsion, digitalization, manufacturing innovation, autonomy, sustainability, and workplace trends. She has more than 20 years of experience in corporate communications, holding leadership positions most recently within the Industrial Capital Goods sector.

Catherine began her career as a marketing writer for a biotechnology company, where she learned to take complicated and highly technical information and make it accessible to everyone. She believes the concept of “storytelling” is more than a trendy buzzword and loves to find ways for her readers to make personal connections to her subjects. Catherine has a passion for technology and innovation and how its intersection can make an impact in all our lives.

Catherine recently moved back to her hometown in the Hudson Valley, New York after a several decades in Los Angeles and Chicago. She is a graduate of UCLA and enjoys gardening and spending time with her husband and three children.

Economic and Operational Benefits of Propane Engines

semi trucks driving on highway

Propane is a low carbon energy source commonly used in millions of homes across the country for cooking, home heating, hot water and many other applications. It can also be used as a clean vehicle fuel in medium duty applications including school buses, delivery and beverage fleets, paratransit vehicles and more.

Thousands of fleet owners choose propane autogas because it offers many environmental, economic and operational benefits. With new technology like the Cummins B6.7 propane engine, fleet owners can experience the power of diesel while producing less greenhouse gas emissions and air pollutants, ultimately saving on operations costs.

Propane is a clean fuel

In testing, the Cummins B6.7 propane engine delivered the lowest greenhouse gas emissions of any propane autogas-powered engine. It will also deliver some of the lowest GHG emissions in the medium-duty market. It is an ultra-low, .02 NOx engine that will meet or exceed EPA and CARB regulations in 2024 and beyond.

For fleets and other end users looking to meet environmental goals, renewable propane is available in the market. It has the same chemical structure and physical properties as conventional propane. It has an even lower carbon intensity than conventional propane because it’s produced from renewable, raw materials. This fuel can be used in any existing propane autogas engine or propane autogas infrastructure. Therefore, fleet owners will be able to easily implement this cleaner energy source in their own vehicles.

Propane is an abundant domestically produced fuel

Approximately 30 billion gallons of propane are produced annually in the United States and about 80% of U.S. propane is produced during the natural gas refining process. Because of that, its price is decoupled from the price of crude oil set by the global market.

Propane is an abundant and portable natural resource in North America. It can be distributed in liquid form using ships, rail cars, trucks and via pipelines. Best of all, propane is an environmentally friendly energy source. When compared with other options like diesel or gasoline, propane can significantly reduce harmful emissions.

Since propane is produced in the U.S., the domestic supply is shielded from global geopolitical and economic shocks. Unlike gasoline and diesel, it provides a reliable energy source for business owners.

Propane engines provide low total operating costs

Due to propane’s widespread and long-standing usage, propane autogas engines are a mature technology. The B6.7 propane engine will be built on Cummins’ fuel agnostic platform, meaning many parts are shared across an array of other engines. This will help reduce cost and complexity to the customer in terms of vehicle acquisition, integration of lower carbon fuel types, and vehicle maintenance.

As a vehicle fuel, propane autogas is affordable and typically costs as much as 50 percent less than diesel. The wholesale cost of propane autogas falls between the price of oil and natural gas, which are the fuel’s two sources. Because of this, propane autogas prices don’t fluctuate as sharply as other fuels, so fleet owners are able to easily manage fuel budgets.

Additionally, there is no need for an exhaust treatment system. That’s because propane is a clean energy source that produces 20 times less nitrogen oxides and particulate emissions than diesel. The B6.7 propane engine is instead fitted with a maintenance-free, three-way catalyst exhaust system.

Due to the cost-effectiveness of the fuel and reduced maintenance costs, propane autogas provides fleet owners with the lowest total cost of ownership. Propane autogas engines like the Cummins B6.7 propane will provide a strong return on investment and a low cost per mile.

Propane engines offer a simple refueling experience

A benefit of propane autogas that many fleet owners may not immediately think about is the ease and affordability of refueling. Fleets can choose from several refueling options. Each one offers distinct advantages that help a company identify and customize a solution that best fits its business and maximizes productivity.

Options range from private on-site stations that are fully scalable to meet the demands of a fleet, to temporary field stations to employ around a site in the field. Some fleets can even use any of the more than 2,800 public refueling stations around the country. Best of all, propane suppliers will often lease the refueling infrastructure to a fleet in exchange for a fuel contract that locks in a set price per gallon for a duration beneficial to both parties.

Fleet owners must consider what energy source will best meet their environmental, economic, and operational needs. With new propane autogas innovations, the Cummins B6.7 propane engine becomes an attractive solution.

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Puneet Singh Jhawar

Puneet Singh Jhawar

Puneet Singh Jhawar is the General Manager of the global natural gas business for Cummins Inc. In this role, he is responsible for the product vision, financial management and overall performance of the natural gas business. Over his 14-year career at Cummins, Jhawar has cultivated successful relationships with a number of Cummins’ largest customers. Jhawar has extensive global experience, with roles based in the Middle East, India, Europe and the US.

How much renewable natural gas is out there?

sun rising over field

There are over 23 million natural gas vehicles in the world, including over 175,000 in the United States. Of these, 64% of all on-road fuel used in these vehicles in 2021 was renewable natural gas (RNG), according to industry trade group, NGV Americas. That percentage increases in California, where it’s 98%. Unlike regular natural gas, RNG is not obtained from fossil resources and constitutes a carbon-neutral or even carbon-negative fuel. However, the amount of available organic feedstock from which RNG can be made is finite. So, how much RNG can be made exactly from existing and potential resources? Let’s take a look.

RNG availability today and tomorrow

RNG is made from biogas, which is the product of a biological process known as anaerobic fermentation. It’s obtained when the undesirable components of biogas, such as CO2 and nitrogen, are removed.

A variety of organic materials feed the biogas-producing bacteria. In many cases, RNG is made opportunistically at facilities which generate a feedstock as a by-product of their operation. Wastewater treatment plants and dairy farms can produce RNG using sewage sludge and manure. Another option is to process food waste into biogas and RNG. Although only are only a few RNG companies, more are seeking to increase production.

The Argonne National Laboratory’s database captures the total annual RNG production capacity in the United States. In 2021, production capacity was about 660 million gallons gasoline equivalents (GGE). That’s a 20% increase compared to the previous year. This is a lot of RNG, yet still just a fraction. -about 3% - of the total natural gas consumption each year in the country, beyond solely vehicles’ consumption. 

It may be possible to increase the production of RNG in the United States—and in other countries—by orders of magnitude. According to a study quoted by the American Gas Association, the US could have the potential to produce up to 36 billion GGE equivalent of RNG each year by 2040. If all of it was used in transportation applications, it would be enough to fuel about two thirds of all diesel vehicles in the country.

How is RNG transported and distributed? 

Producing RNG is only part of the challenge of making RNG more available. RNG also needs to be transported and distributed to end-users. Compared to other alternative fuels, RNG has many advantages. RNG is, chemically, nearly identical to natural gas obtained from fossil resources. Therefore, RNG can be injected into the existing natural gas transportation and distribution infrastructure, as long as it meets each pipeline’s specifications. End users can also purchase RNG from RNG producers and receive natural gas from utility companies. They can claim that they are, effectively, using RNG. In the United States, 3 million miles of distribution lines and over 300,000 miles of transportation pipelines are ready to accept in-spec RNG and deliver it to customers. That’s something which hydrogen producers and users can only dream of. 

How many RNG refueling stations are there?

Finally, RNG needs to make its way into the tank of vehicles. The systems needed to fuel a vehicle with RNG or with fossil natural gas are identical. Both fuels are interchangeable and can be blended. 

However, the network of natural gas fueling stations is less dense than the one for gasoline or diesel. There are about 1,500 public and private stations dispending compressed natural gas in the United States, compared to over 150,000 gas stations with gasoline or diesel. Most of the RNG supply is sent to states with low carbon fuel credits for natural gas. Right now, only California, Oregon and Washington state offer these credits, so suppliers prioritize shipping fuel to them. Fleets can check with their local fuel provider to find out the exact source of their natural gas.  

Businesses who wish to switch their vehicles to RNG often opt to construct a fueling facility on their own premises. These businesses may choose from several categories of fuel pumps dispensing compressed natural gas or compressed RNG. For on-site refueling, most businesses will choose time-fill stations. Time fill systems are best suited for vehicles that can complete a day’s shift on a single tank before ‘going home’ for the night to be refilled. Time-fill stations offer more flexibility and efficiency for fleet managers who can make the most of off-peak electricity rates at night.

Did you know that RNG can offset fuel costs?

RNG can also be produced and used locally. Certain businesses have the option to integrate the production and use of fuel as part of their normal operations. Some waste management companies, for example, gather biogas emanating from landfills they manage. The biogas is refined into RNG, and then used to fuel their garbage collection fleet. This can result in net negative greenhouse gas emissions. The methane emissions that would otherwise make their way into the atmosphere from the landfills are avoided. That’s a huge decarbonization effort considering that methane is greenhouse gas several times more powerful than carbon dioxide, and it’s essentially free fuel for the refuse company.

California leads the way on RNG use and production

RNG made up 98% of the total natural gas vehicle fuel consumption in 2021 in California, according to the government. That’s up from 92% in 2020.

A local waste management company, the City of Perris, operates one of the largest organic waste digesters ever built. Using residential waste such as yard waste and food scraps, it produces about 1 million GGE of RNG every year. Some of that RNG fuels the garbage collection fleet and the rest is sold via an interconnection to the local natural gas network. 

It is not by chance that RNG is so popular in the state. California’s carbon reduction and air quality policies (i.e. Low-Carbon Fuel Standard) have heavily incentivized fleets to use RNG as an alternative to traditional natural gas and petroleum fuels. As other states such as Oregon, Washington and Colorado consider similar rules, the likelihood is high that the appetite for RNG will continue to grow. If you want to learn more, read about the different factors to consider when switching to natural gas engines.

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Puneet Singh Jhawar

Puneet Singh Jhawar

Puneet Singh Jhawar is the General Manager of the global natural gas business for Cummins Inc. In this role, he is responsible for the product vision, financial management and overall performance of the natural gas business. Over his 14-year career at Cummins, Jhawar has cultivated successful relationships with a number of Cummins’ largest customers. Jhawar has extensive global experience, with roles based in the Middle East, India, Europe and the US.

What is the current state of the natural gas refueling infrastructure?

semi parked at natural gas fuel station

In the United States, natural gas is the number one alternative fuel for commercial vehicles. It burns clean and it can help reduce greenhouse gas emissions. Switching to natural gas engines comes with many benefits, but let’s focus on their refueling infrastructure. 
What are the different natural gas production facilities? 

Natural gas is primarily obtained from fossil resources. In the United States, a trend known as the Shale Revolution has caused the domestic production of natural gas to nearly double in 20 years. Natural gas is abundant, relatively cheap, and widely available. This fuel provides natural gas engines with great economic benefits.

Methane, the main constituent of natural gas, can also be obtained in a renewable way by fermenting organic waste. The gas manufactured in that manner is known as renewable natural gas (RNG). RNG can be fully interchangeable with traditional natural gas. The industrial production of RNG is experiencing a boom driven by a growing demand. In 2020, there were 157 facilities producing RNG. By the end of 2021, this number had grown to 230.

How much natural gas is available? 

Natural gas has been used for decades in non-transportation applications. As a result, users and producers can rely on an extensive mid-stream and down-stream infrastructure. This includes pipelines for transportation between natural gas-producing regions and population centers. In most urban and suburban areas, dense distribution networks deliver natural gas into homes and businesses. If you lined up all of the natural gas distribution pipelines in the United States, it would equal 10 times the distance between Earth and the Moon.

While natural gas is almost universally available, it’s not always available for use in vehicles. It is available in compressed form at about 1,500 public and private fueling stations in the United States. There are, in comparison, about 145,000 gasoline stations. Many fleets interested in this technology invest in a private fueling infrastructure so they can fuel up onsite before heading out on routes for the day. This can be a significant investment that not all businesses can afford. With that being said, natural gas vehicles are the least disruptive alternative power technology available today. No radical changes in vehicles or transportation infrastructure is required.

Many natural gas fuel suppliers are also willing to subsidize the fueling infrastructure and recoup the cost over several years with a slightly higher fuel price. 

What do natural gas refueling facilities look like? 

Businesses who do choose to build a Compressed Natural Gas (CNG) fueling station on their premises have several options.

Fast-fill fueling stations receive low pressure fuel from the local distribution network. It then compresses into high-pressure storage vessels. When refueling vehicle, the high-pressure vessel discharges rapidly into the vehicle’s tank. This type of fueling station is best for quick fill-ups and typically used at public-access stations.

Time-fill stations are best suited for heavy vehicles with large tanks that refuel nightly at a central location. These stations receive natural gas at a low pressure from utility companies and the gas is  compressed directly into the vehicle. Time-fill stations tend to be custom-designed. They are designed based on the total number of vehicles, their capacity and the time available to fill them, among other factors. Filling a vehicle at a time-fill station can take up to several hours.

Hybrid combination-fill stations also exist. They incorporate elements from both fast-fill and time-fill systems and offer both options, granting a great deal of flexibility.

Natural gas can also be used in liquid form. Vehicles operating on Liquefied Natural Gas (LNG) require special refueling facilities. LNG stations are less common—there are about 60 in the United States. LNG facilities contain specialty cryogenic equipment, and their use requires certain safety precautions because of the extremely low fuel temperature. LNG stations typically serve long-haul trucking applications. 

How many vehicles are using natural gas?

Natural gas use in motor vehicles has increased over the last six years. From 2016 to 2021, its use has increased by over 230%. New vehicle registrations have also seen growth. In 2021, businesses registered around 6,500 natural gas vehicles. That was a 3% increase from the previous year. There are 121,000 natural gas-powered vehicles on the roads in the United States. Cummins has produced over 85,000 natural gas engines for medium and heavy-duty vehicles. Natural gas engines are good for applications such as transit buses, school buses and garbage trucks.  

If you want to learn more about other aspects of natural gas, don’t forget to also check our answers to frequently asked questions about natural gas engines. These answers cover topics such as cost, practicality, and feasibility of integrating natural gas into commercial fleets.
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Puneet Singh Jhawar

Puneet Singh Jhawar

Puneet Singh Jhawar is the General Manager of the global natural gas business for Cummins Inc. In this role, he is responsible for the product vision, financial management and overall performance of the natural gas business. Over his 14-year career at Cummins, Jhawar has cultivated successful relationships with a number of Cummins’ largest customers. Jhawar has extensive global experience, with roles based in the Middle East, India, Europe and the US.

Environmental sustainability benefits of propane engines

semis driving on a bridge

Liquefied Petroleum Gas, or LPG, is a fuel consisting of a mixture of hydrocarbons, primarily propane and butane. It has been used for decades in a variety of applications, including as a cooking and heating fuel, as a refrigerant fluid in air conditioning systems and as a propellant in aerosol sprays. When it is used as a fuel for motor vehicles, it is sometimes known as Autogas or, simply, as propane.

It is usually obtained by refining crude oil or wet natural gas. Wet natural gas is natural gas that contains an excessive proportion of propane, butane and other non-methane hydrocarbon molecules.

Propane is used in a variety of transport applications including light, medium and heavy-duty vehicles. Its availability and use vary by country. Some countries have promoted the use of propane as a motor fuel as a part of their energy policy. In Turkey, for example, nearly 40% of all passenger vehicles run on propane, according to the World LPG Association. Globally, it’s the third most used fuel, after gasoline and diesel. You can learn more about how LPG compares to natural gas and other fuels.
Propane engines   grant a set of environmental benefits to users. Here are the main ones:

Propane engines reduce Greenhouse Gas Emissions

Propane vehicles can have significantly lower well-to-wheels emissions than gasoline, fossil natural gas and diesel vehicles. Well-to-wheels emissions account for the emissions occurring as a result of the production, transportation and distribution of fuels. When comparing the greenhouse gas (GHG) emissions resulting from the use of different fuels, well-to-wheels emissions are a more meaningful metric than tailpipe emissions. 

Unlike methane, the primary constituent of natural gas, propane is not a GHG. Leaks and other irregular releases during transportation and storage are included in any well-to-wheels accounting, but they make no contribution to global warming. 

A study by the Gas Technology Institute found that school buses running on propane can generate 21% lower well-to-wheels GHG emissions compared to buses running on gasoline. They can also be 7% lower than diesel and 12% lower than compressed natural gas.

Biopropane has a role in decarbonization

Renewable feedstocks, like agricultural waste products, spent cooking oil and animal fats, can also be used to make propane. Biopropane is often co-produced along with biodiesel via complex chemical processes. Chemically, biopropane is nearly identical to propane obtained from fossil resources, so both fuels are interchangeable in many applications. 

The use of biopropane can effectively minimize a vehicle’s carbon emissions like renewable natural gas  or biodiesel. Compared to other biofuels, however, biopropane currently remains a niche-use fuel which is produced in relatively small quantities and has limited availability. As the supply of biodiesel and bio jet fuel grows, so will the supply of renewable propane.

Propane engines reduce emissions from air pollutants

Modern propane engines produce extremely small amounts of NOx. Under certain driving conditions, such as low speed city driving, propane engines will generate less than 4% of the NOx that a comparable diesel engine would produce.

Propane engines also produce almost no soot—only 2% of a diesel engine’s—and very little carbon monoxide. All of this makes propane vehicles intrinsically clean. They are an attractive option for businesses who are required to comply with strict emissions standards such as California’s. Propane engines will also be a great option for those who wish to make a positive impact on the air quality in the communities they reside in. 

Propane is not toxic to the environment

Unlike other petroleum fuels, propane is nontoxic and presents no risk of soil or water contamination. If propane is spilled or leaked outdoors, it will quickly vaporize and harmlessly dissipate into the atmosphere. This makes installing propane fueling stations easy and cost-effective. There’s no  permitting required by the Environmental Protection Agency. It does not affect the ozone layer and, as stated, has very low global warming potential.

Propane may not be an environmental pollutant, but it is a hazardous substance. It is extremely flammable, and, being heavier than air, propane vapors can accumulate into low lying areas. This is why propane vehicles are often not allowed to use underground car parks.

In summary, propane is a great option for clean, environmentally-friendly vehicles. Propane vehicles have extremely low emissions of air pollutants and substantially lower GHG emissions than other vehicles running on other fossil fuels. Propane is also nontoxic, is not a hazard to plant or animal life and will not contaminate the environment. It also delivers the power and range required for many commercial vehicle applications.

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Puneet Singh Jhawar

Puneet Singh Jhawar

Puneet Singh Jhawar is the General Manager of the global natural gas business for Cummins Inc. In this role, he is responsible for the product vision, financial management and overall performance of the natural gas business. Over his 14-year career at Cummins, Jhawar has cultivated successful relationships with a number of Cummins’ largest customers. Jhawar has extensive global experience, with roles based in the Middle East, India, Europe and the US.

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