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:
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.