Light duty vehicles are sedans, pickups and vans. This is how to use NGV in light duty vehicles.
1. Using NGV for sedans (Benzene engine)
These are divided into two types
1.1. Dedicated NGV
These are original equipment manufacturer (OEM). They are designed to use NGV fuel only and have NGV cylinders which are designed to fit in a perfect space.
1.2. Bi-fuel system
Both benzene and NGV fuels can be used and this is determined by a selection switch. This system is OEM or is adapted from the existing benzene engine by installing an NGV engine system. It is divided into two systems.
1.2.1 Fumigation System
The important component for this system is a gas mixer. It functions as a mixer of air and NGV at the precise rate for the right combustion before transmission to the engine. This system is suitable for a carburetor engine. There are two separated gas transmitting regulation systems.
- Open - Loop System This system is the same as the LPG system installed in taxis. There is no electronic control unit (ECU).
- Closed- Loop System This system is installed as an electric control unit (ECU) to regulate the right amount of fuel emission.
1.2.2 Multi Point Injection System or MPI
An electronic control unit is used for this system to evaluate the mass flow of gas before transmitting it to the combustion chamber which operates the same as the benzene engine. This system is good for the benzene engine fuel injection system (EFI).
2. Using NGV for pickup and van (Diesel engine). There are two types of NGVs for diesel engines.
2.1 Dedicated NGV
These are original equipment manufacturer or diesel engine vehicles altered to run on NGV engines.
2.2 Diesel Dual Fuel System (DDF)
This system has been designed to run only on diesel or on both. The ratio of NGV gas and diesel fuel depends on the engine itself and the quality of the CNG equipment used. The advantage of this system is that the vehicle can operate on diesel or on both by using a selection switch. There are two separate systems for emission regulation.
2.2.1. Fumigation Open- Loop System This is called an ordinary system or a mechanic control system. A field study of a pickup using local CNG reveals that the average amount of CNG used in place of diesel fuel is about 25-50 per cent. That means the cost is 15-35 per cent lower. Furthermore; soot and toxic dust are reduced as well.
2.2.2. Fumigation Closed- Loop System Unlike Fumigation Open - Loop System, CNG and diesel fuel emissions are controlled by a computer program. Operation is better, but the price is higher.
For re-powering, an existing diesel engine is removed and replaced with a benzene engine. After that, NGV bi-fuel system equipment is installed. Recommendations in 1.2 should be followed.
2. NGV for heavy duty vehicles
Large NGV vehicles like trucks, trailers and transportation buses can be categorized into 4 types.
1. Original equipment manufacturer (OEM) which are separated into 2 types.
1.1. Dedicated NGV
This type is developed to run on NGV fuel. A spark plug is used in the ignition system. The advantage of this is it leaves less particles of matter in the air. The cost is 20-30 per cent higher than in diesel vehicles. The variance depends on the makes, models, and manufactured groups. In Thailand there is no domestic contribution plant for this, but Cummins are imported from Detroit, America, Daewoo and Hyundai from Korea.
1.2 Diesel Dual Fuel (DDF)
These vehicles' engines are designed to use NGV and diesel fuel. Ignition operates on diesel and combustion system is linked to NGV. Now Caterpillar of America has manufactured engines of this type which run on NGV in place of diesel and can save up to 9 per cent in cost.
2. Improving diesel engines to use NGV fuel
2.1 Diesel dual fuel System (DDF)
Here, without any need to improve the actual engine, NGV equipment can be installed. It means the ignition can be operated, with full combustion, by the diesel engine, then it will operate on NGV. The performance capacity of using diesel and NGV depends on:
- The quality of the existing diesel engine
- The technology and the quality of NGV equipment
- The expertise of the technician
- How it is used etc.
Thus, if high technology is used to tune NGV equipment to take place after diesel combustion, the expense will be lower. This system helps drivers make the best choice between diesel or NGV and diesel fuels by using the selection switch. The approximate distance that is covered before a re-fill of one CNG cylinder of 3-5 tanks of 140 litres of water each, is 300-500 kilometers. There are two fuel emission regulation systems.
2.1.1 Fumigation System
This is called a regular mechanic control or open system. The pressure regulation is maintained at less than 200 bars so the air can be taken into the gas mixer through the intake pipe. When the right ratio of air and NGV is used, the combustion system performs and then is transmitted to the engine. Some makes and models have installed the electronic control unit to regulate the NGV fuel emission to the combustion chamber. The efficiency of the combustion varies depending on the velocity of the engine. Under working conditions, test results of trucks, installed correctly with NGV equipment and running on local NGV fuel reveals an average usage of 25 – 50 per cent less than that of diesel. The highest comparison rate was up to 60 per cent. That means an expense reduction of 15-40 per cent. Furthermore; the amount of toxic particles and soot is also reduced.
2.1.2 Injection System
The pressure regulator reduces pressure in the cylinder to below 200 bars to mix gas with the air in the inlet manifold (single point injection). Then gas is transmitted to mix with air from other intake pipes of each barrel (multi point injection) at a precise ratio for the combustion before transmission to the engine. There are 3 separate types of injections in this system.
1. Single point injection (open -loop).
This is an open system in which NGV and air are mixed in the inductive manifold and fuel emission is controlled by electric control unit (ECU). The NGV regulation will vary depending on the velocity of the engine. The burning quality depends on the perfection of design of the fuel regulation control program.
2. Single point injection (closed- loop).
This system is a single point injection with closing loop. The combustion operates at the inductive manifold as in type a, but NGV fuel emission is controlled by the electric control unit under a computer program. This controls the precise amount of fuel to mix with the air and controls the NGV and diesel to the exact ratio for the right combustion system at different working conditions. Thus, the complete burning of NGV and diesel is satisfied and does not depend on the design of the hose of the injection or the engine sensor devices, such as: oxygen sensor, throttle position sensor etc. or the fuel regulation program or the particular ratio of NGV and diesel.
3. Multi point injection (closed- loop).
The operation system is the same as in b, but gas and air mix in each intake pipe of each barrel. This system performs better, and provides more effective combustion and consumption rate of fuel exhaust emission than other DDF systems. Its price, however, is much more expensive than the others.
2.2 Dedicated retrofit
This involves the modification of the existing diesel engine to reduce the compression ratio from 17:1 to 11:1 by adjusting a barrel, cylinder head and installation of a spark plug for the ignition, also replacement of other equipment that is necessary for each make and model etc. and installation of NGV equipment to operate on NGV fuel. This system vehicle can run only on NGV; diesel can't be used. For the distance of 280-400 kilometres, 5-7 full NGV cylinders (140 litre water size each) are required. Here there are two types of NGV fuel emission systems.
2.2.1 Fumigation system (closed- loop)
The gas mixer is installed with the inlet manifold so gas and NGV are mixed here at the precise ratio for the complete combustion before transmission to the engine. The electronic controlled unit with a computer program is also installed to check the right mass flow of NGV. Effective combustion is controlled by the modified barrel, and the engine contains engine sensors such as: oxygen sensor, throttle position sensor and NGV emission regulation program etc.
2.2.2 Multi point injection system (MPI) with closed -loop
The main components of this system are an electronic control unit, pressure regulator, gas distributor, oxygen sensor and throttle position sensor. CNG is transmitted to each intake pipe of each barrel and the particular ratio of air and gas is controlled by the electronic control unit to operate complete burning (Lambda=1) .The electric control unit receives the signal from the engine sensors and evaluates the emission of NGV to each intake pipe of each barrel to contribute the best combustion. The efficient combustion, the engine operation, the usage rate of the fuel and the exhausted emission are better than the fumigation system with closed- loop, but the price is higher.
Replace the diesel engine with an NGV engine (dedicated NGV) and use the existing chassis. The estimated grand total expense is about 1.0-2.0 million baht. It depends on the makes and models and the horsepower of the engines such as: Cummins, Detroit; NGV Omnitek, Caterpillar in America, Daewoo, Hyundai in Korea, Cummins in China and IVECO in Italy. Installation of NGV equipment is needed. If 5-7 cylinders, each of 140 litres of water are installed, the distance covered will be about 280-400 kilometres.