Introduction

Diesel engines may be converted readily to operate primarily on natural gas, using pilot injection of diesel to achieve ignition.  However, some initial attempts to implement this technology were crude, leading to excessive diesel usage, over-fueling to achieve acceptable power levels, and unacceptably high emissions.  Micro-pilot dual fuel (MPDF) engines show significant potential to rival diesel engines in their part and full load efficiency.  These compression ignition engines operate on a combination of diesel and compressed natural gas (CNG), with a diesel pilot injection igniting a CNG-air mixture.  While they have significant advantages over spark ignited natural gas engines in terms of fuel efficiency, they presently cannot match the low emissions benefits of dedicated SI engines, particularly in their emissions of particulate matter (PM) and oxides of nitrogen (NOx).  This research program is aimed at reducing the emissions from such engines through the adoption of advanced engine control strategies, and at the overall reduction of their diesel fuel consumption.  This research will facilitate the acceptance of these dual fuel engines, increase their market penetration and deployment, decrease their fuel use, and hence reduce dependence on foreign oil imports.  The overall objective of this research is to produce a strategy that will yield high thermal efficiency, low emissions and reduced pilot fuel usage.

This work is being done at the West Virginia University Engine and Emissions Research Center.

An electronic control unit (ECU) is constructed that has been used to run the Navistar T444E engine successfully in diesel-only mode. This West Virginia University designed and built ECU controls fuel injection pulse width (FIPW), injection advance, and injection control oil pressure (ICP). The ECU contains two Microchip PIC based microcontrollers; one to perform initialization of a Silicon Systems 67F687 engine interface peripheral and another to carry out the engine control algorithms while the engine is running. At the present time, the values of FIPW, injection advance, and ICP are set manually using potentiometers located on the ECU.

Control system setup

Navistar Control and Instrumentation   
Block Diagram

Upon review of the control requirements of this project, it was determined that in-cylinder pressure data would be necessary to the development of a control scheme for the engine when running in CNG-diesel dual fuel mode.  A new cylinder head for the Navistar T444E was procured.  The head was adapted to accept in-cylinder pressure transducers.  Two adjacent, centrally located cylinders were fitted with PCB quartz piezoelectric pressure transducers (model number 145A01).  The modified cylinder head was then fitted to the engine.
 

 Cylinder head layout

Location of Sumtak shaft encoder 

Plans for Dual Fuel Conversion

For simplicity, a natural gas intake manifold irrigation system has been chosen.  A trial test has been conducted on dual fuel operation of the engine.  This was done to determine if detonation would be a problem when running natural gas in a high compression (17.5:1) diesel engine.  A natural gas line was simply plumbed into the intake of the engine about three feet before the intake valves.  The flow was controlled with a gate valve operated by hand and the flow was measured with a positive displacement flow meter.  The engine was run at intermediate speed and full load (I100) using only enough diesel to provide 25% of full torque, the engine was then brought to full power by adding natural gas.  Using data from the in-cylinder pressure transducers, it was determined that no detonation was taking place.  Therefore, it appears that no physical modifications to the engine to reduce compression ratio will be necessary although hot operation has not yet been explored.  An IMPCO natural gas control valve as well as low and high pressure regulators have been obtained to do the conversion.
 

This page will be updated as research continues.
 

This page designed by Talus Park