Katerina Swanson
The amount of fuel burned by a car at idle varies depending on a range of factors, including the type of car, the size of the engine, and whether the air conditioning is on. A car generally uses about 0.5 to 1.3 litres of fuel per hour at idle, with the air conditioning increasing fuel usage by around 10%. This means that a car will burn through about a gallon of fuel every four hours of idling.
| Characteristics | Values |
|---|---|
| Average fuel consumption per hour | 0.5-1.3 litres |
| Fuel consumption per hour for compact cars with a 2-liter capacity engine | 0.16-0.3 gallons |
| Fuel consumption per hour for large sedans with a 4.6-liter engine | 0.5-0.7 gallons |
| Fuel consumption per hour for transit buses | nearly 1 gallon |
| Fuel consumption per hour for medium heavy trucks with a GVW of 19,700-26,000 lbs | 0.6 gallons |
| Fuel consumption per hour for diesel medium heavy trucks with a GVW of 23,000-33,000 lbs | 0.4-0.45 gallons |
| Fuel consumption per hour for a BMW 545i | 0.6 gallons |
| Fuel consumption per hour for a 4Runner (3.4L V6) with AC on | 0.6 gallons |
| Fuel consumption per hour for a Civic in good condition | 0.45 gallons |
| Fuel consumption per hour for a Fit with 1.5L | 0.4-0.45 gallons |
| Fuel consumption per hour for a Golf 2.5L 5 cylinder without AC | 0.2 gallons |
| Fuel consumption per hour for a Golf 2.5L 5 cylinder with AC | 0.25 gallons |
| Fuel consumption per hour for a 2001 Acura CL Type S with AC on | 0.5 gallons |
| Fuel consumption per hour for an Audi A3 | 0.7 litres |
| Fuel consumption per hour for an Audi A3 with AC on | 1 litre |
| Fuel consumption per 100 minutes | Engine size in litres |
| Fuel consumption per hour with AC on in winter or summer | 10% more than usual |
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What You'll Learn
Fuel consumption varies with engine size
The amount of fuel a car burns while idling varies depending on several factors, including engine size, air conditioning usage, and vehicle type. On average, a car burns about 0.5 to 1.3 litres of fuel per hour when idling. This rate can increase by approximately 10% when the air conditioning is on.
When it comes to engine size, it is important to understand that the size of an engine is related to the volume of air in the cylinder, to which fuel is added. Air is the dominant factor, and fuel is an additive. Therefore, a larger engine that requires more air per cycle will also require more fuel. This relationship is particularly true when comparing engines with different numbers of pistons, such as a V6 versus an I4 engine. The number of camshafts, valves, and journal bearings can also impact fuel consumption.
However, engine size is not the only factor that determines fuel consumption. The driving style and conditions can also play a significant role. For example, a smaller engine that is pushed to its limits may be less efficient than a larger engine operating comfortably at a higher speed. Similarly, the friction within the engine, measured as friction mean effective pressure (FMEP), can impact fuel efficiency. Higher friction requires more power to keep the engine running, which in turn consumes more fuel.
Additionally, the environmental impact of idling engines should be considered. Idling engines contribute to carbon dioxide emissions, with each gallon of gasoline burned emitting approximately 20 pounds of carbon dioxide. This has serious consequences for the environment, and organizations like Idle Free California aim to reduce idling time to minimize fuel waste and environmental damage.
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Diesel engines and idling
Diesel engines are designed to operate under load, and idling can have several negative impacts on the engine. Firstly, it can lead to increased engine wear due to low cylinder pressure and reduced lubrication, resulting in higher service costs over time. Secondly, unnecessary idling wastes fuel without any productive work, hurting fuel economy and increasing operating costs. This is especially true for large engines, with a study by the Oak Ridge National Laboratory finding that a transit bus consumed nearly 1 gallon of fuel per hour while idling.
Additionally, excessive idling increases harmful emissions such as nitrogen oxides (NOx) and particulate matter, contributing to air pollution. It is important to note that idling can also impact the resale value of your vehicle as the extra hours racked up while idling can negatively affect its resale value.
To reduce the negative impacts of idling, heavy equipment operators and fleet managers can implement a few simple measures. Firstly, try to avoid extended idling during warm-up. Instead, use block heaters to pre-warm the engine coolant, helping the engine reach its optimal operating temperature more efficiently. In colder climates, consider using winter-grade diesel or fuel additives to prevent gelling, reducing the need for long warm-up idling.
Another way to reduce idle times is to set an idle time limit and use an automatic engine shut-off. Many machines idle for a significant portion of their operating time, so using an automatic idling system where the engine speed reduces to idle when the controls are inactive for a set amount of time can help lower idle times.
Finally, it is recommended to allow the equipment to idle for a few minutes to cool down the turbocharger after heavy use. This prevents overheating and prolongs the life of the turbocharger. However, it is important to strike a balance, as excessive idling can be more harmful to diesel engines than many operators realize.
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Environmental impact of idling
Idling vehicles waste nearly 6 billion gallons of fuel per year, costing owners over $20 billion. This wasted fuel has serious environmental consequences. Idle Free California, an organization dedicated to reducing the amount of time that vehicles are left running while parked or stopped, reports that idling wastes an average of 0.9 gallons of fuel per hour in most vehicles. For diesel engines, the amount of fuel used is even higher.
The environmental impact of idling is significant. Every gallon of gasoline burned emits about 20 pounds of carbon dioxide into the atmosphere. This means that idling for one hour generates 17.6 pounds of CO2 emissions. When employees are out on deliveries or service calls, it is important to remind them to turn off the engine when they have to wait for more than 10 seconds at each stop. Even a few minutes of idling can quickly add up, and good driving habits, such as turning off the engine whenever possible, can make a big difference.
The data on fuel consumption and emissions from idling vehicles highlights the environmental impact of wasted fuel. The large amount of fuel wasted by idling vehicles contributes to increased carbon dioxide emissions, which have negative consequences for the environment. Reducing idling time can help to mitigate these environmental impacts and reduce fuel costs for vehicle owners.
Additionally, idling vehicles contribute to air pollution, particularly in urban areas with high traffic density. Idling engines release various pollutants, including nitrogen oxides (NOx), particulate matter (PM), and volatile organic compounds (VOCs). These pollutants can have detrimental effects on human health and the environment. Prolonged exposure to emissions from idling vehicles has been linked to respiratory problems, cardiovascular issues, and other adverse health effects in vulnerable individuals.
The environmental impact of idling vehicles extends beyond fuel waste and emissions. It also contributes to air pollution, affecting the health and well-being of individuals, particularly in densely populated areas. By raising awareness, implementing policies, and adopting better driving habits, we can reduce the environmental and health impacts associated with idling vehicles.
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Cost of idling
The cost of idling a car depends on several factors, including the size of the engine, fuel efficiency of the car, and the price of fuel. Idling for extended periods can waste fuel and increase costs for drivers and fleet operators.
According to Idle Free California, idling wastes an average of 0.9 gallons of fuel per hour in most vehicles. This can add up to significant costs over time. For example, if you leave your light-duty truck running for 20 minutes each day, that adds up to 18 gallons of wasted fuel per year. This equates to almost one full tank of gas, assuming a fuel efficiency of 15 miles per gallon. The costs are even higher for diesel-powered vehicles.
The Argonne National Laboratory conducted a study on three different engines: a 1.8-liter Honda Civic, a 2.5-liter Ford Fusion, and a 3.6-liter Chevrolet Malibu. They found that idling for 10 minutes consumed between $0.08 and $0.41 worth of fuel, depending on the engine size and fuel price. At $2.90 per gallon of gasoline, this translates to a cost of roughly $0.08 to $0.41 for every 10 minutes of idling.
For larger engines, the costs can be even higher. If you have an engine bigger than 3.6 liters and idle for 10 minutes each day during the winter, you could spend over $50 in fuel over the season. In contrast, using a 1,000-watt plug-in car heater to warm up your car and defrost your windshield would cost roughly 16 cents per hour, making it a more cost-effective option.
It is worth noting that idling also has serious environmental consequences. Every gallon of gasoline burned emits about 20 pounds of carbon dioxide into the atmosphere. Idling for one hour generates 17.6 pounds of CO2 emissions. Therefore, it is essential to remind drivers to turn off their engines when waiting for extended periods, as this can help reduce both fuel costs and environmental impact.
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Sensors and desired engine speed
The amount of fuel burned by a car idling depends on several factors, including the type of engine and fuel, the length of time the car is idling, and the desired engine speed. Sensors play a crucial role in maintaining the desired engine speed while minimising fuel consumption.
Various sensors provide critical feedback to the idle speed control system. These sensors include those that measure throttle valve position, manifold pressure, and engine speed. For example, a crankshaft speed sensor is used in a closed-loop control system to regulate the idle speed to a desired value. Additionally, battery sensors can measure voltage, current, and temperature, providing valuable data for idle speed control.
The desired idle speed is typically set at a lower RPM than the normal production idle speed. For instance, Yurkovich and Simpson (1997) proposed a control model that set the desired idle speed at 611 RPM, which is lower than the standard idle speed of 740 RPM. This reduction in idle speed contributes to minimising fuel consumption.
To maintain the desired engine speed, the idle speed control system may employ different methods. One approach involves regulating the mass airflow with the throttle command from the driver at zero. This requires a small but non-zero throttle angle to achieve the desired airflow. Alternatively, some engines utilise a special air passage that bypasses the throttle plate to achieve the desired airflow for the idle RPM.
In summary, sensors play a crucial role in idle speed control systems by providing valuable feedback on various parameters such as throttle valve position, manifold pressure, and engine speed. By adjusting the desired engine speed and utilising different control methods, the idle speed control system aims to minimise fuel consumption while maintaining stable engine operation.
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Frequently asked questions
A car generally uses about 0.5 to 1.3 litres of fuel per hour at idle. This depends on the car, with a compact car burning around 0.16-0.3 gallons of gas per hour, and a large sedan burning 0.5-0.7 gallons of gas per hour.
Yes, using the air conditioning increases the amount of fuel burned by around 10%.
Idling wastes fuel and money, with an average of 0.9 gallons of fuel burned per hour. This amounts to around \$20 billion in fuel costs per year.
