Originally Posted by ROBERTSUNRUS
Hi, A few words for some of you and some facts. Minnie's Mate, Shame on you for driving so fast. [75 MPH] And I'm not too far behind you with my set up consistantly averageing 11.5 MPG. As for the pipe thing, not meant to be offensive. SORRY. Bill Tex, Please check that Lincoln.com site again. I think you will find out that my 2000
Lincoln Navigator With 5.4 Litre, V-8, 32
-Valve, Dual Overhead Cam,
Engine has more torque at a lower RPM than the engine you looked up. Also could you count the moveing parts on your Diesel and show where it is less? That is if you compare a push rod Diesel to a push rod gas engine? And for sake of agreeing with the rest of you; Yes the Diesels are torque monsters, but I still don't like them for reasons stated earlier. And you should respect my opinion for that just as I respect your love for your Diesel. I did not tell anyone they should not have Diesels. I just gave my opinion.
Correction 355 ft.lbs torque at 2750 RPM for my engine.
Bob, see below for a basic explanation of the differences of diesel vs gasoline engines. Many more moving parts in gas engines.
Diesel engines get better fuel economy simply because they do not need to burn as much fuel as a gas engine to get the same power. Diesel engines are also built heavier than a gas engine to sustain the added stress of the higher compression ratio. Diesel engines do not have an ignition system so you will never have to tune them up. Exhaust systems last longer because diesel fuel exhaust is not as corrosive a gasoline engine exhaust.
It is not unusual to see a diesel engine with 400,000, 500,000 and I have even seen them go as much as 600,000 miles.
You are right, I could not find specs about the older Navigator With 5.4 Litre engine. I erred on the side of caution and quoted the latest specs available. I am not saying everyone who tows needs a diesel. If you are towing a lighter load, for short distances, it would be difficult to justify. If you travel frequently, as we do, it becomes much more pleasurable. I have towed with a couple of 1/2 ton gas Suburbans (similiar to your Navigator). There is no comparison for me-I'll take the diesel.
developed the idea for the diesel engine and obtained the German patent for it in 1892. His goal was to create an engine with high efficiency
. Gasoline engines had been invented in 1876 and, especially at that time, were not very efficient.
The main differences between the gasoline engine and the diesel engine are:
- A gasoline engine intakes a mixture of gas and air, compresses it and ignites the mixture with a spark. A diesel engine takes in just air, compresses it and then injects fuel into the compressed air. The heat of the compressed air lights the fuel spontaneously.
- A gasoline engine compresses at a ratio of 8:1 to 12:1, while a diesel engine compresses at a ratio of 14:1 to as high as 25:1. The higher compression ratio of the diesel engine leads to better efficiency.
- Gasoline engines generally use either carburetion, in which the air and fuel is mixed long before the air enters the cylinder, or port fuel injection, in which the fuel is injected just prior to the intake stroke (outside the cylinder). Diesel engines use direct fuel injection -- the diesel fuel is injected directly into the cylinder.
Note that the diesel engine has no spark plug, that it intakes air and compresses it, and that it then injects the fuel directly into the combustion chamber (direct injection). It is the heat of the compressed air that lights the fuel in a diesel engine.
The injector on a diesel engine is its most complex component and has been the subject of a great deal of experimentation -- in any particular engine it may be located in a variety of places. The injector has to be able to withstand the temperature and pressure inside the cylinder and still deliver the fuel in a fine mist. Getting the mist circulated in the cylinder so that it is evenly distributed is also a problem, so some diesel engines employ special induction valves, pre-combustion chambers or other devices to swirl the air in the combustion chamber or otherwise improve the ignition and combustion process.
One big difference between a diesel engine and a gas engine is in the injection process. Most car engines use port injection or a carburetor rather than direct injection. In a car engine, therefore, all of the fuel is loaded into the cylinder during the intake stroke and then compressed. The compression of the fuel/air mixture limits the compression ratio of the engine -- if it compresses the air too much, the fuel/air mixture spontaneously ignites and causes knocking
. A diesel compresses only air, so the compression ratio can be much higher. The higher the compression ratio, the more power is generated.
Some diesel engines contain a glow plug
of some sort (not shown in this figure). When a diesel engine is cold, the compression process may not raise the air to a high enough temperature to ignite the fuel. The glow plug is an electrically heated wire (think of the hot wires you see in a toaster
) that helps ignite the fuel when the engine is cold so that the engine can start. According to Cley Brotherton, a Journeyman heavy equipment technician:
- All functions in a modern engine are controlled by the ECM communicating with an elaborate set of sensors measuring everything from R.P.M. to engine coolant and oil temperatures and even engine position (i.e. T.D.C.). Glow plugs are rarely used today on larger engines. The ECM senses ambient air temperature and retards the timing of the engine in cold weather so the injector sprays the fuel at a later time. The air in the cylinder is compressed more, creating more heat, which aids in starting.
Smaller engines and engines that do not have such advanced computer control
use glow plugs to solve the cold-starting problem.
If you have ever compared diesel fuel and gasoline
, you know that they are different. They certainly smell different. Diesel fuel is heavier and oilier. Diesel fuel evaporates much more slowly than gasoline -- its boiling point is actually higher than the boiling point of water. You will often hear diesel fuel referred to as "diesel oil" because it is so oily.
Diesel fuel evaporates more slowly because it is heavier. It contains more carbon atoms in longer chains than gasoline does (gasoline is typically C9
, while diesel fuel is typically C14
). It takes less refining
to create diesel fuel, which is why it is generally cheaper than gasoline.
Diesel fuel has a higher energy density
than gasoline. On average, 1 gallon (3.8 L) of diesel fuel contains approximately 155x106
joules (147,000 BTU), while 1 gallon of gasoline contains 132x106
joules (125,000 BTU). This, combined with the improved efficiency of diesel engines, explains why diesel engines get better mileage than equivalent gasoline engines.
Inside a typical car engine
Almost all cars today use a reciprocating internal combustion engine because this engine is:
- Relatively efficient (compared to an external combustion engine)
- Relatively inexpensive (compared to a gas turbine)
- Relatively easy to refuel (compared to an electric car)
These advantages beat any other existing technology for moving a car around.
Almost all cars currently use what is called a four-stroke combustion cycle
to convert gasoline into motion. The four-stroke approach is also known as the Otto cycle
, in honor of Nikolaus Otto, who invented it in 1867. The four strokes are illustrated in Figure 1
. They are:
Understanding the Cycles
- Intake stroke
- Compression stroke
- Combustion stroke
- Exhaust stroke
Here's what happens as the engine goes through its cycle:
- The piston starts at the top, the intake valve opens, and the piston moves down to let the engine take in a cylinder-full of air and gasoline. This is the intake stroke. Only the tiniest drop of gasoline needs to be mixed into the air for this to work. (Part 1 of the figure)
- Then the piston moves back up to compress this fuel/air mixture. Compression makes the explosion more powerful. (Part 2 of the figure)
- When the piston reaches the top of its stroke, the spark plug emits a spark to ignite the gasoline. The gasoline charge in the cylinder explodes, driving the piston down. (Part 3 of the figure)
- Once the piston hits the bottom of its stroke, the exhaust valve opens and the exhaust leaves the cylinder to go out the tail pipe. (Part 4 of the figure)
5.Now the engine is ready for the next cycle, so it intakes another charge of air and gas. Notice that the motion that comes out of an internal combustion engine is rotational
, while the motion produced by a potato cannon is linear
(straight line). In an engine the linear motion of the pistons is converted into rotational motion by the crank shaft. The rotational motion is nice because we plan to turn (rotate) the car's wheels with it anyway.
In order to fully grasp the differences between diesel and gasoline engines, you must look at the similarities first. Both engines contain cylinders, and the number of cylinders is determined by the make of the car. These cylinders can be arranged in
three different ways, which are inline, V, or flat. All three of these configurations have their advantages and disadvantages, making them more effective in certain cars then others. In an inline configuration, the cylinders are arranged in a line in a single bank. In
a V formation, the cylinders are set at opposing angles to form a V to each other. Finally, a flat, or horizontal or boxer, has cylinders horizontally opposed to it.
Both engines have a relatively similar combustion cycle. The cycle is four strokes long, or
four times the piston changes linear direction. The strokes are the intake stroke, the compression stroke, the combustion
stroke, and the exhaust stroke. During the intake stroke, the piston moves down in time with the opening of the intake valve.
This allows the cylinder to become full of an air and gas mixture. This mixture is compressed during the compression stroke,
which increases the compression pressure at which the gas mixture will be ignited, or self-ignited. The combustion stroke is the
stroke following the explosion of the mixture, and this stroke is what powers the car. It is this stroke that powers the
crankshaft, and allows for the car to move. The fin
al stroke is the exhaust stroke. The exhaust valve opens when the piston
hits the bottom, and the piston pushes the exhaust out.
Inside these cylinders, there are pistons that travel the length of the cylinder. These
pistons create the compression ratio that is needed to successfully ignite the fuel and air
mixture, and also directly transfer the explosion power to the crankshaft. This crankshaft is
essential to the engine because it takes the pistons linear motion, and turns into circular
motion that can be utilized by a car.
Both engines also have camshafts, which operate the opening and closing of valves. The more modern cars have overhead cams, which means the valves are directly below the camshaft and has less moving parts, which increases engine efficiency over a camshaft that is located in the sump, or near the crankshaft. The timing of the valves is also key to a properly running engine. A timing belt links the crankshaft to the camshaft so that the valves are in sync with the pistons. The valves control the entering and exiting of fuel, whether it is before or after combustion has occurred. The number of valves can increase performance as well, and many high-performance cars have two v
alves for intake, and two for exhaust. The added potential volume of fuel that can be injected, and the increased volume for exhaust to escape, creates a more explosive combustion ratio of fuel to air, and allows for the piston to operate on a fresh fuel and air mixture each time, which increases efficiency as well. If you take a mathematical approach to this, a cylinder that has a set volume will have restriction on the size of valves that can be used with it. If an engine has two valves total, then:
Surface area of cylinder=1
Radius of cylinder=v1/?
Radius of valve=(v1/?)/2
Surface area of valve=(v1/?)/2)2 ?
=1/4 per valve or 1/2 for two valves
When you evaluate four valves, you get a valve that has an area of .17, but when you consider the total area of the valves, you .68, which is an 18% increase.
The main difference between a gasoline engine and a diesel engine is obviously the fuel used. The main difference between these fuels is the combustion ratio at which each will explode. Gasoline does not self-ignite when compressed, because it does not generate enough heat. It needs activation energy to explode, and this energy is generated by a spark plug at the top of the cylinder. Diesel on the other hand, does not require a spark plug to ignite it because it generates enough heat when it is completely compressed to ignite itself and cause explosion. The compression pressure is directly related to the combustion as well. Diesel engines have a much higher compression pressure than gasoli
ne engines. The higher compression pressure in diesels explains the difference in the methods of ignition used in gasoline and diesel engines. The reason for this higher pressure is that in a diesel engine, only air is compressed. The fuel is then directly injected into the cylinder, and this allows for a much higher compression ratio.
The makeup of both gasoline and diesel is different as well. Gasoline is typically C9H20, while diesel fuel is typically C14H30. The increase in carbon and hydrogen atoms is the reason the energy density of diesel is greater as well. On average, 1 gallon (3.8 L) of diesel fuel contains approximately 155x106 joules (147,000 BTU), while 1 gallon of gasoline contains 132x106 joules (125,000 BTU).
The question then is, which engine is “better”. By better I mean more efficient, powerful, and faster. There are four different types of efficiencies to consider in an engine, and they are cycle, thermal, mechanical, and volumetric.
The efficiency of any cycle, be it a gasoline or diesel cycle, is equal to the output divided by the input. The efficiency of
the diesel cycle is higher than the gasoline cycle because of higher compression ratio, and because the temperature of
combustion in a diesel engine is much higher. Therefore, the heat input in a diesel engine is at a higher average temperature. The
higher temperature is outweighed by the increased heat output at that same temperature. A gasoline engine cannot have the
same compression ratio as a diesel engine, because fuel and air are mixed before they reach the cylinder, and they would
explode before the piston reached the correct firing position, causing the engine to “knock” and not exploit the most efficient
use of energy. It is true then that a diesel engine is more cycle efficient.