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 20 different diesel engine models
to dual fuel 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 Development
Process
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.
Dual fuel engine development
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:
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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.
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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.
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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.
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Design dual fuel conversion system including the
mechanical hardware equipment, electronic hardware
and the engine management requirement.
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Application
of the kit components to the engine for diesel,
gas, air and other engine management sensors as
required.
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Test and
characterise the diesel injector pump and develop
a Pump table.
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Select
appropriate gas injector design and appropriate
gas Orifice table combination.
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Correctly establish each of the almost 400 software
settings.
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Select
catalytic converter if required. |
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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.
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Dynamometer testing the engine
on gas to compile the Gas, Diesel and Air Fuelling
Tables to meet Requirements Specification.
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Emissions
testing to establish emissions performance. Iterative
tuning to confirm emissions requirements have been
met.
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Testing the combination of fuelling tables, settings
and calibration for use on the road.
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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.
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Acceptance that the engine meets the Requirements
Specification and signing off by the client and
DieselGas.
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Commissioning
of at least one engine in the vehicle and the establishment
of a road trial.
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Client
or third party emissions tests if required.
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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 can 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.
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
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. 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. Roof
mounting of cylinders should only be undertaken at the
factory.
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 programmes 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:
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Design
and installation of storage cylinder systems and
interconnecting pipe work, valves, intercooler etc.
to the vehicle. |
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Installation
of conversion kit or installation of converted engine
to the vehicle and commissioning of the vehicle.
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Initial
road trials to prove the engine and vehicle operation.
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Chassis
dynamometer testing to confirm Power and torque
using local gas. Modification and adjustment as
required to meet the requirements.
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Begin
extended road trials.
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Production engineering
Upon completion of the prototype
demonstration and road trials the new system components
and the engine installation need to be assessed as to
their suitability for production. This includes suitability
of design and cost of manufacture, engine and vehicle
installation and equipment service. This process will
take place once the product has been accepted for production. |
