Dual fuel engine development

May 2003
DUAL FUEL CNG CONVERSION PROGRAMS
By DieselGas of New Zealand
Overview
For many years DieselGas, have been aware of the severe pollution problems experienced in many cities and the aim of Governments to reduce this problem. It has been quoted that 70% of the atmospheric pollution in many large cities is caused by diesel exhaust emissions. DieselGas is an alternative fuels, equipment, development company that specialises in technology to convert diesel engines to operate on dedicated compressed natural gas (CNG) and dual fuel (Diesel/CNG). This paper concentrates on dual fuel conversions.
Benefits of Experience
Our New Zealand engineers have converted more than 25 different diesel engine models to dedicated gas operation and more than 35 diesel engine models to dual fuel operation. The Yellow Bus Company in Auckland New Zealand has converted more than 80 buses to dedicated natural gas and these vehicles have in total travelled more than 20 million kilometres of successful commercial operation.

DieselGas expertise includes a diverse mix of skills, knowledge and experience as well as a unique Engine Management System and Technician Interface Software programme. This technology implemented in co-operation with engine manufacturers or local engine specialists ensure Project Objectives are met.
Diesel Engine Conversion Process
Application Engineering (AE)
CNG Engine Background.
Diesel engines employ compression ignition to ignite the diesel fuel in the combustion process. Dual fuel engines use the compression ignition of a small pilot injection of diesel, to combust the gas ingested into the combustion chamber with the inlet air.
The maintenance of controlled stable combustion is the heart of good dual fuel conversions.

What is Application Engineering (AE)
Application engineering incorporates all of the mechanical changes, electronic changes and the addition of the gas and diesel control equipment to allow the engine to operate successfully on gas. It also includes the testing and documentation required to confirm the engine performance and to allow the conversion kit to be released as a pre-production prototype.

Diesel Engine Conversion to Dual Fuel Operation
Diesel engines converted to dual fuel require few mechanical changes to the engine but considerable dynamometer development time during the AE process. The AE process includes.
? Establish a Requirements Specification to be agreed by the client and DieselGas. This will include power and torque, plus emissions performance on both diesel and dual fuel.
? Instrumentation and thorough testing of the engine on diesel prior to conversion to obtain accurate power and emissions performance records. These records are used as the benchmark by which to compare the performance of the engine in gas operation.
? For electronic diesel engines the engine management control algorithms and ECU inputs and outputs are required. If these are not available from the engine manufacturer they will need to be reverse engineered by dynamometer testing.
? Design dual fuel conversion system including the mechanical hardware equipment, electronic hardware and the engine management requirements.
? Application of the kit components to the engine for diesel, gas, air and other engine management sensors as required.
? Test and characterise the diesel injector pump and develop a Pump table.
? Select appropriate gas injector design and appropriate gas Orifice table combination.
? Correctly establish each of the almost 400 software settings
? Select catalytic converter if required.
? Implement the DieselGas engine management system to control the variable parameters of the engine including diesel, gas and air/fuel ratio control, injection timing and automatic switching to diesel operation and various safeties.
? Dynamometer testing the engine on gas to compile the Gas, Diesel and Air Fuelling Tables to meet Requirements Specification.
? Emissions testing to establish emissions performance. Iterative tuning to confirm emissions requirements have been met.
? Testing the combination of fuelling tables, settings and calibration for use on the road
? Implement the Engine Management System Technician Interface software programme, which uses MS Windows from a laptop computer. This includes Automatic fault detection, Self diagnostics and Fault Logging with Graphing program to analyse Fault Logs and statistical logging. The Fault Log records 15 seconds of engine operation prior to the Fault. These Fault and other Logs can easily be sent electronically to the factory for analysis and rapid diagnosis of problems.
? Acceptance that the engine meets the Requirements Specification and signing off by the client and DieselGas.
? Commissioning of at least one engine in the vehicle and the establishment of a road trial.
? Client or third party emissions tests if required.
General
Other aspects to be taken into account when converting engines to dual fuel operation are ambient temperature variation, inlet manifold air temperature (aftercoolers are required for all turbocharged dedicated gas and dual fuel engines), altitude plus gas and diesel temperature composition.
Gas Quality
Gas composition will have a significant affect on performance of the engines on gas. Accurate reporting of the gas composition and any variations to the composition is vital to the success of the project.

It will be necessary to have accurate gas composition records. These will be required at the commencement of the engine design process. The information will be required for each of the gas supplies where the vehicles are intended for use. If the gas is found to vary significantly it may be necessary to design the conversion systems for the least acceptable gas which may also mean compromising engine performance.

Kit Manufacture and Supply
The pre-production prototype design, produced as part of the AE, will be used to develop a production design and to procure, manufacture and supply further engine conversion kits. Procurement of fuel storage cylinders and other high pressure components will complete the vehicle conversion.
Other general conditions
Local Facilities
It will be the responsibility of the client to establish facilities suitable for the commissioning and testing of engines and vehicles.
Engine Conversion
The engine AE programme will be undertaken at DieselGas. It is possible for client engineers and technicians will be involved in AE of the diesel engines as part of a training programme.
Vehicle Conversion
For large fleets of vehicles the local engineers will undertake the installation of the cylinders and pipe work on the vehicle and also the installation and commissioning of ongoing vehicles.

Condition of Vehicles for Conversion
All engines and vehicles provided for conversion must either be in first class working order or brought up to an agreed standard before work commences on the conversion. The right of inspection and rejection of vehicles not up to this standard is reserved by DieselGas.

Storage Cylinders
It is recommended that steel cylinders be mounted underneath the chassis on vehicles for all retrofit conversions. If the storage cylinders are roof mounted on buses, then lightweight composite cylinders must be used, and the bus framework must also be strengthened to suit. However, we believe that the high costs associated with roof mounting of cylinders may be found to be prohibitive.

Engineering Support
Engineering support for all facets of the project will be available directly from DieselGas New Zealand. This includes fax, phone and electronic mail as well as personal visits.

The DieselGas Technician Interface Software supports the DieselGas Engine Management System. The System is designed for use with dedicated gas engines and dual fuel engines. The Technician Interface Software is a user friendly programme which uses MS Windows on a laptop computer. It includes Automatic fault detection, Self diagnostics, statistical logging and Fault Logging with Graphing programme to analyse Fault Logs. It includes extensive Help files to assist with correcting faults. The Fault Log records 15 seconds of engine operation prior to a Fault being Logged. These Fault Logs can easily be sent electronically to the factory for analysis and rapid remote diagnosis of problems. Statistical logging allow for long term analysis of the engine and vehicle performance.

Initial and ongoing training will provide technical staff with a full understanding of the system designs, service and maintenance techniques.
Training
The transference of training techniques and expertise by DieselGas will be aimed at tutor training. These tutors will train local technicians. A good training programms is essential to the success of the project. The training will include vehicle conversion techniques, service and maintenance. The training can be part of the AE programme and during vehicle commissioning.

Refuelling Facility
CNG/LNG must be readily available for refuelling vehicles for dynamometer and road trials.
Standards
All equipment and engineering services supplied shall comply with Vehicle Standard AS/NZS2739:1999 for CNG conversion equipment and systems unless otherwise stated.

Engine Performance.
The converted engines shall have performance ratings similar to the performance of an equivalent diesel engine in terms of the power and torque developed providing the natural gas meets a minimum specified standard and consistency.

Exhaust Emissions.
Exhaust emissions are very engine specific and will depend to a great extent on the emissions performance of the engine in diesel mode. Emissions standards vary considerably as do the goals of clients when considering the reduction of emissions. Significant reduction in both Greenhouse and local emissions are possible on dual fuel engines.
Dual fuelling generally shows a substantial reduction in CO2 exhaust emissions compared to diesel engines. Substantial reductions in NOx can be achieved with some increase in CO. THC will increase but NMHC are generally similar to diesel performance. The reduction in PM on dual fuel will be up to 90% on older engines and less on modern diesel engines.
Choosing an emissions target that is affordable, satisfies the client goals and is attainable using the chosen engine, is part of the Requirements Specifications
Third party validation can be undertaken at the cost of the client.
Initial Vehicle Conversion
Once a kit has been released for road testing a prototype vehicle will be road trialled locally. This initial conversion and road trial may involve:

? Design and installation of storage cylinder systems and interconnecting pipe work, valves, intercooler etc. to the vehicle.
? Installation of conversion kit or installation of converted engine to the vehicle and commissioning of the vehicle.
? Initial road trials to prove the engine and vehicle operation.
? Chassis dynamometer testing to confirm Power and torque using local gas. Modification and adjustment as required to meet the requirements.
? Begin extended road trials.