The Case For Diesel

The Basics of Diesel Technology Diesel engines have long proven to be a reliable, economical and durable source of power for many applications. Diesel engines work on a different platform than petrol or other technologies, relying on compression instead of spark to ignite a mixture of air and diesel fuel. The mixture of air and fuel is constantly changed to directly respond to the load placed on the engine. For this reason, diesel technology is ideal for commercial applications because of its ability to provide performance and power that is efficient, economical, durable, and reliable.

Diesel Fuel Characteristics
1. More energy - diesel fuel contains more energy per unit volume than petrol
2. Safer - the less volatile diesel has a higher flash point and is far less likely to ignite or explode if spilled or released
3. Better Fuel Economy up to 45% to 60% better fuel economy can be achieved when combined with the more efficient combustion process of the diesel engine.

Environmental impact
The environmental performance of diesel engines is one of continuous improvement. Significant advances in diesel engine technology have resulted in considerable improvements in diesel emissions. Because of the greater efficiency of diesel engines and the significant fuel economy advantage, diesel engines emit 30 - 35 per cent fewer carbon emissions than petrol. This is good news because the effects of carbon-based greenhouse gasses emission on the global climate and temperature patterns are an increasing concern.

Decrease in Total Overall Emissions
The US has reported an overall decrease in diesel emissions over the past 10 years, resulting largely from the rapid development of diesel technology and diesel engine technology.

1. On-Road Diesel Engines:
- Total NOx emissions from on-road diesels dropped by 25% (oxides of nitrogen)
- Total S02 emissions from on-road diesels dropped by 76% (sulfure dioxide)
- Total PM-10 emissions from on-road diesels dropped by 37% (coarse particulate matter smaller than 10 micrometers in diameter)
- Total PM-2.5 emissions from on-road diesels have dropped by 35% (fine particulates smaller than 2:5 micrometers in diameter)

2. Off-Road Diesel Engines:
- 25% reduction in particulate emissions from off-road diesels over the last 25 years

The Diesel Engine
Diesel engines are workhorse engines, powering heavy-duty trucks, buses, tractors, trains, large ships, bulldozers, cranes, and other construction equipment. The diesel engine's image as a muscle-bound monster has now given way to vastly improved engines that delivers more fuel, efficiency, more fuel flexibility, and cleaner emissions.

How Diesel Engines Work
A diesel is an internal combustion engine that converts chemical energy in fuel to mechanical energy that moves pistons up and down inside enclosed spaces called cylinders. The pistons are connected to the engine's crankshaft, which " changes their linear motion into the rotary motion needed to propel the vehicle's wheels. Energy is released in a series of small explosions' as fuel reacts chemically with oxygen from the air. This is where diesel and gasoline differs.

Gasoline engines start the explosions with sparks from spark plugs. In diesel engines, fuel ignites on its own.

Air heats up when it is compressed. This fact led German engineer Rudolf Diesel to theorize that fuel could be made to ignite spontaneously if the air inside an engine's cylinders became hot enough through compressions. Achieving high temperatures meant producing much greater air compression than occurs in gasoline engines. High compressions could lead to high engine efficiency. Part of the reason is that compressing air concentrates fuel-burning oxygen. A fuel that has high energy content per gallon, such as diesel for example, will react with most of the concentrated oxygen to deliver more power per explosion when injected into the engine's cylinders at exactly the right time.

These calculations proved to be correct. Consequently, even though vast improvements have been made on diesel engines over the years, the basic concept of the 4-stroke diesel engine is still unchanged. The first stroke involves drawing air into a cylinder as the piston creates space for it by moving away front the intake valve. The piston's subsequent upward swing then compresses the air, heating it at the same time. Next, fuel is injected under high pressure as the piston approaches the top of its compression stroke, igniting spontaneously as it contacts the heated air.

The hot combustion gasses expand, driving the piston downward in what is called the power stroke. During its return swing, the piston pushes spent gases from the cylinder, and the cycle begins again with an intake of fresh air.

How Diesel Engines Have Improved
Older diesel engines mixed fuel and air in a pre- combustion chamber before injecting it into a cylinder. The mixing and injection steps were controlled mechanically, which made it very difficult to tailor the fuel-air mixture to changing engine conditions. This led to incomplete fuel combustion, particularly at low speeds. As a result, fuel was wasted and tailpipe emissions were relatively high.

Today's diesels inject fuel directly into an engine's cylinders using tiny computers to deliver precisely the right amount of fuel the instant it is needed. All functions in a modern diesel engine are controlled an electronic control module that communicates with an elaborate array of sensors placed at strategic locations throughout the engine to monitor everything from engine speed to coolant and oil temperatures and even piston positions. Tight electronic control means that fuel burns more thoroughly, delivering more power, greater fuel economy and fewer emissions. Modern direct-injection diesel engines producer low amounts of carbon dioxide, carbon monoxide, and unburned hydrocarbons. Emissions of reactive nitrogen compounds (NOx) and particulate matter (PM) have been reduced since 1980. Nevertheless, NOx and PM emissions remain at relatively high levels.

What Improvements Need To Be Made?
Diesel engines are already more efficient than their gasoline counterparts (45% vs. 30%). Further advances (55% to 63%) are possible. Widespread use of diesel engines, particularly in trucks, vans and sport utility vehicles promises to substantially reduce dependence on petroleum products.