SHED Testing for the Automotive IndustryApril 24, 2019
In the United States, we go through about 392 million gallons of gasoline every day. It’s no wonder that you seem to hear discussions about fuel emissions and its effects on our health and environment on a near-constant basis. It can be easy for some people to see the automotive industry as a careless contributor to pollution, but the reality is that the automotive industry as a whole is committed to minimizing harmful emissions and to making driving a car safe, both in the short- and long-term.
When most people talk about emissions, they’re likely focusing on fuel exhaust emissions. These are the emissions that vehicles produce as they burn fuel. However, there is another type of emissions that are worth our focus — evaporative emissions. Just ask the Environmental Protection Agency (EPA), which has extensive regulations related to these emissions.
In this post, we’re going to take some time to explain what evaporative emissions are and what we can do to minimize their effects. In particular, we’re going to focus on SHED testing, a type of testing that can help you measure various evaporative emissions so you can effectively design individual components and whole fuel systems to comply with emissions regulations and contribute to a cleaner, safer world.
What Are Evaporative Emissions?
Before we talk about SHED testing, let’s talk about why this sort of testing is necessary. SHED testing is intended to make sure vehicles aren’t emitting too many fuel vapors. So, what are fuel vapors, and why should we keep them from entering into the air?
Gasoline is composed of hundreds of various hydrocarbons, which are volatile organic compounds (VOC). As gasoline or other types of fuel undergo the natural process of evaporation, they emit vapors into the air. There’s nothing wrong with evaporation when the vapors that enter the air are harmless, such as in the case of water. However, fuel vapors are pollutants that can harm our air quality and our health.
For example, when nitrogen oxides (NOx) combine with hydrocarbons in sunlight, they produce ozone. When ozone is high in the atmosphere, it protects the planet from ultraviolet radiation. However, holes in the ozone layer can let ozone get closer to the surface, where it can promote smog.
Air pollution from vehicles can cause or contribute to many health problems, including:
- Birth defects
- Eye irritation
- Heart disease
- Other respiratory issues
We’ll talk more about the specific health concerns related to evaporative emissions later in this post.
With our modern understanding of the harmful effects of evaporative emissions, we’ve developed more efficient exhaust emission controls and formulated gasoline to be less harmful. That said, evaporative emissions can still occur and pollute the air in a few different ways, including:
- Resting loss: As temperatures rise during the day, especially in warmer climates and in the summertime, gasoline sitting in the fuel tank of a parked car can begin to evaporate. This type of emission is also known as diurnal emission.
- Running loss: When your car is running, the engine is likely anywhere from 195 to 220 degrees Fahrenheit. At this temperature, the engine and exhaust system will vaporize gasoline. Another term for running loss is crankcase emissions.
- Hot soak: Even after you’ve parked your car and turned it off, the engine will stay hot for a while. During this time, even though your car is no longer running, evaporative emissions will continue.
- Refueling: Another instance when evaporative emissions can be a problem is at the gas station. When you refuel, as your gas tank is filled with liquid gasoline, it forces out fuel vapor through your vent pipe.
All of these sources of evaporative emissions are cause for concern because they are largely unavoidable. Some researchers focus on attempting to uncover just how hazardous these issues are. One study from 2015, for example, focused on the issue of evaporative emissions at gas stations, examining just how hazardous this problem is to human health and the environment.
What Is an EVAP?
So, what can be done about evaporative emissions? Engineers in the automotive industry know that the first line of defense against this problem is the evaporative emission control system (EVAP). Without an EVAP system, there would be nothing to keep a multitude of dangerous hydrocarbons from directly entering into our atmosphere.
Evaporative emission control systems are required on all vehicles today. These systems are designed to keep evaporative emissions from polluting the air by sealing off the fuel system from the atmosphere. An EVAP may look different depending on the vehicle it’s a part of, but generally, it is comprised of the following components:
- Fuel tank: Modern fuel tanks are made with extra room at the top, so when fuel expands on a hot day, the EVAP system won’t leak.
- Gas cap: Whereas older gas caps were designed to vent, modern gas caps are completely sealed off.
- Vapor canister: The EVAP canister is a small container filled with activated charcoal. This charcoal absorbs fuel vapors and stores them until the engine is running. Once the car is running, the vapors are drawn out of the canister and into the engine.
- Liquid-vapor separator: Because the EVAP canister is only equipped to store vapors, the liquid-vapor separator keeps liquid gasoline from getting into the vent line that leads to the EVAP canister.
- Rollover valve: This part of the EVAP is specifically designed to keep fuel from leaking in the event of an accident where a vehicle rolls over.
These parts are all connected by various lines and hoses that allow vapor and liquid fuel to travel where it needs to go and remain contained within the EVAP system.
What Is SHED Testing?
Equipping a vehicle with an EVAP system isn’t enough if you don’t test the vehicle to see whether it’s emitting harmful hydrocarbons into the air. This is where SHED testing comes in. SHED is an abbreviation for sealed housing evaporative determination. As the name suggests, this testing method involves placing a vehicle or component in an enclosure and determining the level of evaporative emissions that are coming from it.
Mini and micro SHEDs are designed to test small parts or smaller vehicles like motorcycles or ATVs. Though you can test individual components with SHED testing, one of the unique advantages of a SHED test is that it can test an entire vehicle at once. This allows engineers to get an accurate picture of how effective a fuel system is at keeping harmful hydrocarbons from entering into the air. The picture is especially accurate because the way a SHED test can simulate real-life conditions, which we’ll talk more about in the next section.
SHED testing has been around for many decades, but it has become more critical in recent years as emissions laws have become more stringent. These laws will only become even stricter in the coming years as the EPA and other influential standard-setting bodies take greater measures to protect our environment from hydrocarbons and other types of harmful emissions. As laws become stricter, SHED testing will take on even greater importance.
How Is This Testing Performed?
So, how is a SHED test performed? The answer depends on which type of emissions you want to test for. Remember, there are four different types of evaporative emission losses a fuel system can experience. In every case, however, these tests take advantage of the SHED apparatus. This testing apparatus is an air-tight structure that contains ambient air. It’s critical that it doesn’t allow air in or out so that you can accurately measure the amount of hydrocarbons in the air inside the enclosure.
Earlier SHED tests simply consisted of measuring the difference in hydrocarbon levels from the beginning of a test to the end. However, more recent regulations place more of a focus on the influence of temperature on evaporative emissions. Therefore, modern SHED tests involve maintaining a specific temperature within the testing chamber. Sometimes, these tests are referred to as VT SHED for variable temperature sealed housing for evaporative determination. Testers put a vehicle through several SHED tests to check the efficiency of the EVAP system under various temperature conditions.
For even more accurate results, a SHED testing chamber should be equipped to account for pressure changes that naturally occur from the change in temperature. They do this by introducing or evacuating small portions of ambient air to and from the testing chamber. Done correctly, this is an effective way of maintaining a constant level of pressure in the air.
Of course, introducing new air or taking out some of the ambient air in the chamber could affect the levels of hydrocarbons in the air. This is why the air used to maintain pressure is also measured and factored into the final measurement of hydrocarbons.
The basic means of deriving results is calculating the mass in the chamber from the density, concentration and volume at the beginning and end of the test. The change in mass indicates how many grams of emissions entered the air. The Environmental Protection Agency’s Protection of the Environment regulations Section 86.143–96 specifies exactly how to calculate the amount of evaporative emissions.
As we mentioned, there are four basic types of evaporative emissions losses to watch out for. Let’s review these in light of SHED testing:
- Resting loss: By manipulating the temperature, diurnal tests conducted in a SHED testing chamber can simulate the temperature fluctuations that happen over a day or multiple days. For example, a three-diurnal test involves three heat builds over the course of 72 hours.
- Running loss: A running loss test is more straightforward than a diurnal test. It just involves running the engine for several hours and then measuring the amount of evaporative emissions in the air.
- Hot soak: Since hot soak emissions can evaporate into the air immediately after a car has been running, this test should occur within seven minutes of a hot start exhaust test. For a hot soak test, the temperature in the chamber must be between 68 and 86 degrees Fahrenheit.
- Refueling: Evaporative emissions from refueling must be measured through other tests. The SHED test does not involve a human subject inside the testing chamber.
Why Is This Testing Important?
There are a few critical reasons why SHED testing is important. Let’s take a moment to look at the three main reasons SHED testing is valuable and even necessary:
1. Legal Regulations
Perhaps first on the list for automotive engineers and manufacturers is the fact that federal law demands vehicles stay within certain boundaries for evaporative emissions. The strongest authority on this is the EPA. Because of our growing awareness of the dangers of hydrocarbons, which we’ll discuss more in the next two reasons for SHED testing, the EPA continues to update their regulations, making them increasingly strict.
Before you can successfully bring a vehicle to market, you must make sure the vehicle complies with all relevant regulations. Emissions testing of various kinds is essential to confirm that a vehicle complies with regulations and is safe for drivers to take on the road. Because SHED testing can simulate real-life circumstances that can contribute to evaporative emissions, it’s an invaluable means of checking the efficacy of a vehicle’s EVAP.
2. Environmental Concerns
One of the major reasons for legal regulations surrounding evaporative emissions is that they contribute to air pollution, which harms the environment. Specifically, you may hear that the VOCs from evaporative emissions contribute to smog. Smog is a nickname for a combination of pollutants that is comprised primarily of ground-level ozone.
Smog has some serious health effects, as we’ll see in the next reason, but it also has a severe effect on the health of our planet. It can stunt the growth of plants and damage forests and crops. Some scientists also claim smog has contributed to climate change. Modern efforts to heal our environment from past damage and prevent further damage are often focused on the transportation sector as it is a major contributor to air pollution.
3. Human Health
As we already alluded to, human health is also a major concern when it comes to evaporative emissions. This is because airborne hydrocarbons are known to have some negative health effects on humans, particularly when they undergo a chemical reaction to form nitrogen dioxide (NO2) and ozone (O3). Nitrogen dioxide, in particular, is known to cause respiratory problems.
Nitrogen dioxide may also indirectly contribute to issues like pulmonary disease and increased susceptibility to infections, among other health complications. Just as regulations surrounding evaporative emissions seek to protect the environment, they also seek to protect people from the hazards of inhaling pollutants.
What Standards Need to Be Met?
For several decades, Americans, along with members of other developed nations all over the world, have been concerned about the quality of our air and how it may be affecting our health and our environment. The Clean Air Act, which initially passed in 1970, was an early attempt to reduce air pollution in the United States. The Act has undergone multiple amendments that have updated its mandates to require vehicles to limit the amount of pollution they cause.
In the late 1980s, the EPA became increasingly concerned about the way fuel emissions specifically contribute to smog and air pollution. The EPA is the chief standard-setting body when it comes to evaporative emissions in the United States. However, another influential body is the California Air Resources Board (CARB). Because of the climate and volume of vehicles that are driven in Los Angeles, the federal government allows CARB, with EPA approval, to publish its own, more stringent standards for emissions. Some states choose to enforce CARB standards where they are stricter than the EPA’s.
It is smart for automotive companies to be aware of the most current regulations, including any regulations that are more difficult to meet than the EPA’s. The more benchmarks your vehicles meet, the wider the market you can sell those vehicles to.
So, what are the current standards? The EPA has regularly updated its standards for the automotive industry and published these standards so manufacturers and consumers alike have access to the current regulations. The EPA’s current regulations have come in a series of phases, or tiers, with each one cracking down more significantly on emissions, including evaporative emissions.
To give an idea of the current standard, the Tier 3 emission standard is strict enough that a leak as small as 0.02 inches in a fuel system would likely fail a SHED test by a significant margin. Even a small leak like this could cause the system to emit four to five times more emissions than is allowed daily.
The exact regulations depend on the type of vehicle and model year. There are also different standards for different SHED tests. For example, a new passenger vehicle must emit no more than 0.05 grams during a four-hour diurnal test. During a four-hour running test, it can’t emit more than 0.2 grams of hydrocarbons and methanol. The standards for two- and three-day evaporative emission tests range anywhere from 0.3 grams to 0.5 grams for light- and medium-duty passenger vehicles.
Make sure you are aware of the standards that apply to the vehicle you’re testing. Heavy-duty vehicles or vehicles that run on diesel fuel have different standards from the ones we’ve looked at briefly here. If you outsource your vehicle testing, make sure the testing company is well-versed in all current regulations and is committed to helping you comply with those regulations.
How Can NTS Perform These Tests?
At NTS, we understand just how extensive the regulations are that affect the automotive industry. We can help you meet them so you can get your vehicle to market. We work alongside your engineering team to solve problems fast. Even though we work efficiently, we never compromise on quality. When you trust NTS to conduct SHED testing, you can feel confident that we’ll carefully follow EPA-regulated test procedures and derive accurate results, every time.
Our state-of-the-art testing facilities, scattered all over the United States, allow us to conduct all sorts of tests, including evaporative emissions testing and other types of automotive testing. From mechanical tests and vibration tests to various emissions tests and more, we have the expertise and the equipment to get the job done with accuracy and excellence. Our Detroit location is especially well-equipped to handle a wide range of automotive testing.
We don’t just have the necessary knowledge for conducting tests. Our experts stay on top of all trends and evolutions affecting the automotive manufacturing industry. We are committed to being the kind of partners you want — familiar with the goals and challenges that influence what you do every day and how you strive to become the best of the best.
We offer a comprehensive solution for your automotive testing needs, so get in touch with us today. You can request a free quote now to learn more about how we can help get your vehicle on the road and maintain your reputation for quality and environmental responsibility.