Alternative Fuels

Switching from Diesel to CNG or LNG Fueled Engines

Key components to consider before transitioning to alternative fuel-based vehicles.

Over the past several years, more and more American refuse haulers have been considering the change from diesel to either CNG (compressed natural gas) or LNG (liquefied natural gas) fueled engines in their collection fleets. Gas engine fact: There are more than 28,000 engines in service in the refuse industry worldwide. This article will discuss the some components to consider before transitioning to alternative fuel-based vehicles.

Driving Change

Three key components that can drive change to alternative fuel-based vehicles.

#1: Environmental Leadership

Natural gas has a simple chemical makeup: one molecule of carbon and four molecules of hydrogen (CH4). That’s what makes it burn so cleanly. Other fuels such as diesel are more chemically complex. This means that to meet 2010 EPA emissions requirements, diesel engines need sophisticated vehicle emissions control devices. However, natural gas fueled vehicles do not require complex after-treatment because of the inherently “clean” nature of the fuel. Increasingly, natural gas is being regarded as a cleaner and more environmentally responsible fuel choice.

#2: Economic Benefits

Today, gaseous fuels such as natural gas are available at a significantly lower cost than diesel fuel. Also, the option to lock in low fuel prices for several years can be an attractive option for many businesses that deal with multi-year contracts. Converting a fleet from diesel to natural gas can provide a huge economic advantage for the hauler. The more trucks a hauler runs and the more fuel they burn, the larger the advantage.

There are some arguments on the other side of the fence as well. Natural gas engines may be slightly less efficient (ten to fifteen percent) than an equivalent diesel engine and maintenance costs may be a little higher. Overall, in the right situation, the total cost of ownership (TCO) of a vehicle powered by a natural gas engine is lower than a diesel equivalent.


#3: Federal Energy Policy

The U.S. consumes approximately 21 million barrels of oil a day and most of the supply comes from outside the U.S. That is a large amount of the U.S. dollars that leave the U.S. economy. On the other hand, the U.S. is the world’s largest producer of natural gas. We have the ability to supply our own fuel needs for many years and keep the money in our economy.

America will decrease its dependency on foreign oil and the accompanying pricing volatility that is associated with the oil market. Within North America we are fortunate to have large untapped natural gas resources — 2.6 trillion CF at last estimate — enough to supply our needs for more than 100 years. We also have the ability to capture landfill gas for use in vehicle fuel (biomethane or renewable natural gas [RNG]). Which in effect, turns waste into “green” energy will be nothing but positive for the U.S. We are embracing the opportunity to use our own natural resources in a manner that is both cost effective and more environmentally conscious.

CNG Benefits


Natural gas pricing is significantly lower than diesel. In addition, there are federal and state funding programs offered to haulers to assist in offsetting incremental costs for the transition. The federal government currently provides subsidies of approximately fifty cents a DGE (diesel gallon equivalent) to all fleets using natural gas as a vehicle fuel source. Some states also provide incentives by way of grants to help compensate for the additional costs associated with the purchase of natural gas vehicles.

Noise Control

One diesel engine idling is noisier than ten gas engines. A natural gas engine is much quieter than a diesel engine.


Emissions control systems comparable for natural gas engines are less complicated and weigh less than those required for 2010 diesel engines. Gas engines do not require active after-treatment such as diesel particulate filters or selective catalytic reduction. Also because they don’t need diesel exhaust fluid (DEF), no additional tank system is needed on the truck to store these fluids, maintain their temperature, and sense levels. Gas engines use a simple, maintenance free three-way catalyst. Unlike the diesel engine, gas engines don’t have a DPF, therefore don’t need regeneration on a regular basis or require driver input to operate the emissions systems.

Making the Switch

After you have researched and investigated all the facts and have decided to start the changeover, there are still a few things to keep in mind when making the switch.

Driver Education

As of today, there are only a few viable offerings in the U.S. market for a natural gas engine for a collection vehicle. There are limits to horse power and torque for this engine in this application. The manner in which these trucks are geared can overcome most of these limitations, but your operators should be made aware of the differences in comparison to diesel.

A CNG or LNG engine truck performs differently compared than its diesel cousin. Traditionally there is a slight decrease in horsepower and torque over a diesel engine. The driver/operator needs to understand these differences. Some companies offer onsite training as well as mobile classrooms to help drivers and operators through transition steps. Look into these options when getting ready to make the change.

Fueling Sources

Does your fleet have readily accessible, reliably priced CNG or LNG? Or, will you be building a fueling station at your site?


Gas engines use different oil than diesel engines. If the fleet runs both diesel and gas engines, there is a need to make sure that the correct engine lubrication oil is available. If drivers top off their own oil as part of their pre- or post-trip maintenance they need to be trained to use the correct engine oil.

In addition, the change intervals for spark plugs in the currently available gas engines are more frequent than a diesel injector. Remember to add these costs into your maintenance projections.

Fuel Quality

All CNG/LNG trucks should be equipped with a fuel filter, readily accessible to the driver/operator. As part of the daily pre- or post-trip this filter will need to be drained. There is a tap on the bottom of the filter to allow for easy draining. Training should be part of the haulers protocol to ensure that the driver/operator understands the need for this operation. It’s a good idea to also inspect what comes out of the filter. For example, a significant quantity of oil in the CNG fueled system may point to excessive oil carry over from the CNG compressor from the fueling source and needs to be addressed. Oil on CNG engine intake sensors can cause performance issues and costly repairs that may not be covered by warranty.

There are differences in determining the oil change intervals between natural gas engines and diesel engines. Work with the engine company support staff to set oil drain intervals so that the engine manufacturer warranty is not affected.

In conclusion, there are many advantages to using CNG/ LNG fueled vehicles in refuse applications, many of which can immediately be seen. While many manufacturers are beginning to enter the alternative fuel market, doing your homework before implementing a plan is essential when considering making the switch. It will streamline the process and make it less stressful.

Andrew Simon is Marketing Coordinator for Autocar (Hagerstown, IN). He can be reached at (765) 489-6049, via e-mail at or visit