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Light duty diesels
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In US legislation, the light duty vehicle (LDV) category includes all vehicles of less than 8,500 lbs (3,859 kg) gross vehicle weight rating (GVWR, meaning vehicle weight plus rated cargo capacity). LDVs are further divided into the following sub-categories (w1):

  • passenger cars

  • light light-duty trucks (LLDT), below 6,000 lbs GVWR

  • heavy light-duty trucks (HLDT), above 6,000 lbs GVWR

In Europe, vehicles of less than 3,500 kg gross vehicle weight belong to the light-duty sector and vehicles with more than 3,500 kg GVW are referred to as heavy duty vehicles (HDVs). Light-duty vehicle (LDV) technology is derived from passenger car developments, though the higher vehicle weight requires more engine power.

Conventional light diesel trucks produce significant amounts of pollutant emissions - especially particulate matter (PM) and nitrogen oxides (NOx) - that cause a deterioration of air quality. In typical light trucks at present, these emissions are controlled primarily through improvements to the basic engine, rather than through the use of aftertreatment devices (other than diesel oxidation catalysts in limited applications.) These control techniques are usually limited by a NOx and PM tradeoff, where strategies to reduce one pollutant will result in an increase to the other.

NOx formation is directly dependent on the temperature. Increased combustion temperatures result in increased NOx. Therefore, NOx control in an engine is accomplished by reducing peak combustion temperatures and the duration of these high temperatures in the combustion chamber. PM, on the other hand, is primarily the result of the incomplete combustion of diesel fuel. Control technologies to reduce PM generally focus on improving combustion of the fuel, which results in higher combustion temperatures and NOx. Some strategies currently used to control both diesel NOx and PM emissions include turbocharging, aftercooling, combustion chamber design changes, injection timing retard, and high pressure fuel injection.

Advanced diesel engines and emission control systems are starting to emerge in industrialized countries. . As examples the following features could be included separately or in combination in the exhaust emission control system. These are also addressed in the New Trucks Advanced Heavy Duty Diesels section.

  • Direct injection (DI)

  • Optimal combustion chamber shape and intake air rotation

  • Turbo charging (compressing intake air above ambient conditions)

  • Intercooling

In addition, the use of the following aftertreatment devices can be applied to reduce emissions further, which are discussed in more detail in the New Trucks Advanced Light Duty Diesels:

  • Diesel particulate filters (DPFs)

  • CRT, the continuously regenerating trap

  • Diesel oxidation catalysts (DOCs)

  • Selective catalytic reduction (SCR) systems

  • Exhaust gas recirculation (EGR) systems

These technologies require or profit from the use of low sulfur diesel.

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The turbocharger reduces both NOx and PM emissions by about 33%, compared to a naturally aspirated engine. The turbocharger boosts the pressure (and temperature) of the air entering the engine. This allows more fuel to be added to increase power output, while still inhibiting PM formation. The power to drive the turbocharger is extracted from the engine's exhaust stream. In other words the turbocharger increases engine power and efficiency, which may translate to lower emissions.

Intercooling of the turbocharged air results in even greater NOx and PM reductions, by decreasing the temperature of the charged air after it has been heated by the turbocharger during compression. Cool air is denser than hot air and, therefore, this approach complements the turbocharger by further improving cylinder filling.

Combustion chamber design includes modifications to the shape of the chamber, location of the injection swirl, crevice volumes, and compression ratios. These can result in significant NOx and PM reductions by changing the conditions that occur during fuel combustion.

Injection timing retard is used to reduce the peak flame temperature and, thus, NOx emissions. However, timing retard typically lowers efficiency, resulting in increased fuel consumption and PM emissions. High pressure fuel injection can regain some of the efficiency loss by improving the atomization of the fuel spray and air utilization, resulting in more complete combustion.

A thorough discussion of these technologies can be found in document (1) "Air Pollution from Motor Vehicles - Standards and Technologies for Controlling Emissions", Asif Faiz, Christopher S. Weaver, Michael P. Walsh, 1996, 266 pages .

The development and improvement of the emission control technologies listed above were induced by tightened emission standards in North America, Europe and Japan. They led to a drastic reduction of toxic pollutant emissions from vehicles over the last few decades. This trend is continuing through successively tighter emission standards in many parts of the world. The DieselNet (w2) lists such standards for the US, Europe, Japan and Latin America, as well as certain other countries worldwide. These standards essentially reflect the emission reduction potential to be achieved by emission control technologies for light duty vehicles. US federal regulations treat diesel and gasoline powered cars in the same way from 2004 onwards. Currently there exists a more relaxed NOx limit for diesels (w2). In Europe, emission standards for diesel and gasoline powered vehicles are different at present. It is however considered within the EU to consolidate these standards for EURO V in 2010.

As noted earlier, engine manufacturers design engines with a variety of factors in mind including costs, performance, fuel economy and emissions as well as other factors. Different engines, therefore, while complying with the same emissions standards (e.g., Euro 2) may utilize very different combinations of the above measures to achieve each engine's given market niche. Different manufacturers may also employ fundamentally different philosophies, believing for example that they have a competitive advantage with one technology versus another. Therefore in considering the discussion above, the important message is that there are a variety of technologies which have emerged and have been used by manufacturers to fulfill the emissions regulations of the market where the engine has been or will be sold.

The table below shows the evolution of European emission standards for light commercial vehicles from 1994 through 2006.

EU Emission Standards for Light Commercial Vehicles, g/km (w3)

Class Tier Year CO HC HC+NOx NOx PM

Diesel

N1<1305 kg

Euro 1

1994.10

2.72

-

0.97

-

0.14

Euro 2

1998.01

1.0

-

0.60

-

0.10

Euro 3

2000.01

0.64

-

0.56

0.50

0.05

Euro 4

2005.01

0.50

-

0.30

0.25

0.025

N21305-1760 kg

Euro 1

1994.10

5.17

-

1.40

-

0.19

Euro 2

1998.01

1.2

-

1.1

-

0.15

Euro 3

2002.01

0.80

-

0.72

0.65

0.07

Euro 4

2006.01

0.63

-

0.39

0.33

0.04

N3>1760 kg

Euro 1

1994.10

6.90

-

1.70

-

0.25

Euro 2

1998.01

1.35

-

1.3

-

0.20

Euro 3

2002.01

0.95

-

0.86

0.78

0.10

Euro 4

2006.01

0.74

-

0.46

0.39

0.06

Note: For Euro 1/2 the weight classes were N1 (<1250 kg), N2 (1250-1700 kg), N3 (>1700 kg).Measured in the New European Driving Cycle (NEDC)

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Diesel combustion systems have been used in the transport sector for many decades and are considered to be very reliable. Advanced engine systems are only now entering the market, their reliability in long-term daily use remains to be assessed. Experiences with the durability of the various aftertreatment devices can be found in the retrofit heavy truck systems section.

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Cost estimates are contained in Document (1) "Air Pollution from Motor Vehicles - Standards and Technologies for Controlling Emissions", Asif Faiz, Christopher S. Weaver, Michael P. Walsh, 1996, 266 pages

In a report for congress in October 2000 (w3), it was stated that the "EPA predicts that the new regulations (the "Tier 2" standards, which will be phased in between model year 2004 and 2009) will cost less than $100 per vehicle for most passenger cars, less than $200 for most light trucks, and approximately $350 for larger passenger trucks, with no increases in the cost of vehicle care and maintenance. In the public comment period, it was argued that EPA did not look at diesel-fueled light-duty vehicles specifically, and that per vehicle costs for diesels could be as high as $1,000. In response, EPA contends that while diesel costs were not specifically addressed, additional costs will be negligible compared to gasoline vehicles".

Some additional costs result from the necessity of low sulfur diesel fuel (for optimal operation of most aftertreatment devices).

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The technologies listed above are now for the most part well established on the European and North American markets. For experiences with the various diesel aftertreatment devices, see also the retrofit bus section.

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Diesel technology is reliable and durable. It is important to assure that they receive the appropriate fuel and lubricants and necessary maintenance.

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