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Heat engines are energy conversion machines—they convert chemical energy in a fuel into work by combusting the fuel in air to produce heat. This heat is used to raise the temperature and pressure of a working fluid that is then used to perform useful work. Heat engines can be classified as:
Engines can also be classified as either reciprocating or rotary:
In internal combustion (IC) engines, the working fluid consists of air, a fuel-air mixture or the products of combustion of the fuel-air mixture itself. Reciprocating piston engines are perhaps the most common form of internal combustion engine known. They power cars, trucks, trains and most marine vessels. They are also used in many small utility applications. They can be fueled with liquid fuels such as gasoline and diesel fuel or gaseous fuels such as natural gas and LPG. Two common sub categories of reciprocating piston engines are the two-stroke and the four-stroke engine. Examples of rotary internal combustion engines include the Wankel rotary engine and the gas turbine.
Common goals in the design and development of all heat engines include: maximizing work (power output), minimizing energy consumption and reducing pollutants that may be formed in the process of converting chemical energy to work. Figure 1 shows the main components of reciprocating internal combustion engines. The trunk engine design is the most common—though the term “trunk engine” is rarely used outside of the large engine industry. The crosshead design is currently used only in large low-speed two-stroke engines. Intake and exhaust valves are omitted for simplicity, however it is worth noting that in some two-stroke engine designs inlet and exhaust ports are used rather than valves.
Both two- and four-stroke reciprocating internal combustion engine may be equipped with either a spark-ignited (SI) or a compression-ignited (CI) combustion system.
Conventionally, spark-ignited systems are characterized by a pre-mixed charge (i.e., fuel and air are mixed prior to ignition) and an external ignition source such as a spark plug. Pre-mixing can occur in the intake manifold or in-cylinder. While the pre-mixed charge has a relatively homogeneous spatial distribution of air and fuel in most applications, the distribution can also be heterogeneous. Combustion is initiated by a spark and the flame propagates outwards along a front from the spark location. Combustion in SI engines is said to be kinetically controlled because the entire mixture is flammable and the rate of combustion is determined by how quickly the chemical reaction can consume this mixture starting from the ignition source.
Conventional diesel engines are characterized by fuel injection directly into the cylinder approximately at the time ignition is required. As a result, the charge of air and fuel in these engines is very heterogeneous with some regions being over-rich and others being over-lean. Between these extremes, a mixture of fuel and air will exist in varying proportions. Upon injection, the fuel evaporates in this high temperature environment and mixes with the hot surrounding air in the combustion chamber. The temperature of the evaporated fuel reaches its auto-ignition temperature and ignites spontaneously to start the combustion process. The auto-ignition temperature of fuel depends on its chemistry. Unlike the SI system, combustion in compression-ignited engines can occur at many points where the air-fuel ratio and temperature can sustain this process. The bulk of the combustion process in CI engines is said to be mixing controlled because the rate is controlled by the formation of ignitable mixtures of air and fuel in the combustion chamber.
The distinction between SI and CI engines can be blurred in some cases. Due to pressures to reduce emissions and fuel consumption, combustion systems have been developed that can use some of the features of both SI and CI engines; for example, spontaneous ignition of premixed mixtures of gasoline, diesel fuel or a mixture of the two.
Gas turbines, Figure 2, are another example of internal combustion engines. However, unlike reciprocating piston engines, combustion occurs separately in a dedicated combustion chamber.
In external combustion engines, the working fluid is entirely separated from the fuel-air mixture. Heat from the combustion products is transferred to the working fluid through the walls of a heat exchanger. The steam engine is a well known example of an external combustion engine.
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An example of a reciprocating external combustion engine is the Stirling engine where heat is added to the working fluid at high temperature and rejected at low temperature. Heat added to the working fluid can be generated from practically any heat source, such as burning fossil fuels, wood, or any other organic material.
The Rankine cycle upon which many steam engine designs are based is another example of an external combustion engine. Heat added from an external source elevates the temperature of a liquid, such as water, until it is converted into vapor that is used to move a piston or spin a turbine. Steam engines powered cars in the USA between and ; however, they all but disappeared by . Steam powered trucks were popular in England until the mid-s. While steam powered locomotives in many countries were gradually replaced by diesel locomotives over much of the 20th century, a few remained in main-line service well into the 21st century. Reasons for the demise of the steam engine as the prime mover in mobile applications included the size and number of the major components required for their operation such as furnace, boiler, turbine, valves, as well as their complicated controls [422]. The steam turbine—still in operation in many stationary power plants—is an example of a rotary external combustion engine.
In the 21st century, the focus on improving engine efficiency has created renewed interest in the Rankine cycle for mobile applications—in the form of exhaust waste heat recovery (WHR). While some of these devices use steam, others use organic fluids that are better suited for applications with relatively low vehicle exhaust temperature. Due to the combination of the Rankine cycle and an organic working fluid, these systems are often referred to as Organic Rankine Cycle (ORC) waste heat recovery systems.
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Sometimes, you know what’s wrong with your car immediately when you hear certain sounds or see fluids on the ground. However, sometimes, you get a warning light that doesn’t make sense. This is one of the signs that you need an engine diagnostic, which you can get from your Ford dealership. Here are other signs you need to get your engine diagnosed.
Even though you might be able to self-diagnose your car if you hear a certain sound, such as squealing brakes, there are some sounds you might not recognize. For example, if you hear a rattling coming from under your hood, it could indicate several different problems. This is an ideal reason to get your car diagnosed at your dealership’s service center. They’ll be able to tell you right away what’s making the rattling noise.
Smelling strange odors is never a good sign when it comes to your car, but sometimes, you can tell where the smell is coming from. For instance, if you’re driving down a steep hill and you are riding your brakes, you may smell a burnt odor from the brakes overheating. On other occasions, though, you may smell gas or other odors that you can’t identify. Bring your car into your dealership to figure out where the smell is coming from.
It can be difficult to determine what causes your electronics to not work properly, as it can be anything from your alternator to your battery to your computer system. A factory-trained technician at your dealership can use their diagnostic tool to determine why your electronics aren’t functioning correctly. They’ll also be able to repair or replace the part that is causing the issue with genuine manufacturer parts to keep your car performing at its best.
Your vehicle should always immediately respond when you press on your accelerator, but if you depress the pedal and nothing happens for a second or two, something is wrong. Again, this can be traced to a number of mechanical issues, so it’s hard to diagnose without the proper equipment. A technician can hook your car up to the diagnostic tool for your specific car and be able to tell you what’s wrong right away.
While steam coming from your tailpipe is normal, especially during cold days, if you see black or blue smoke coming from the tailpipe, there’s something not right in your engine. Colored smoke is never a good sign when you’re driving a car, so this needs to be diagnosed as soon as possible to prevent further damage to your engine.
Just as you should get your body examined every year at your doctor’s office, you’ll want to get your car an annual check-up as well. Having your car diagnosed annually will identify problems early, before they’ll require more extensive repairs. If there’s nothing wrong, it will give you peace of mind that your car is running just as it should.
Don’t put off having your engine diagnosed, especially if you notice any of the above signs. Contact Jack Madden Ford to schedule your diagnostic appointment today!
Photo courtesy of Ford
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