Lean burn engines have in general a higher compression ratio, higher power to cylinder volume ratio, and lower emissions than stochiometric engines. Lean burn engines without an electronic air to fuel ratio will experience emissions swings (predominantly NOx) due to ambient, aftercooler temperature or gas quality changes. Modern lean burn gas engines can experience misfire e3 leanburn overviewor detonation due to these changes.
Lambda Control International (LCI) personal have many years of experience in lean burn gas engine air to fuel ratio retrofit for large, medium and small engines, providing off the shelf and customized solutions. An air to fuel ratio system upgrade is generally done to enhance the engine performance, operate the engine on a particular fuel or simply to comply with emission legislation. Typical is that an air to fuel ratio system upgrade automatically results in emission control, even though this might not have been the initial reason.
An air to fuel ratio control’s main focus is to provide a specific amount of fuel for the air consumed. It provides a constant environment for the sparkplug to fire and significantly minimizes risk to detonation and misfire. The air fuel ratio control maintains combustion temperature and provides constant specific fuel consumption. The combustion temperature is directly related to NOx-emission level.
A very cost-effective way of lean burn air fuel ratio control is using the feedback signal from the generator kW-transducer. Literally thousands of engines with some over 25 years of operation are operating with generator feedback, which Woodward has patented as Gas Quality Closed Loop. This algorithm is available in all EGS01/EGS02/E3/E6 and PG+ Lean burn gas engine solutions.
Generator feedback is available for:
1. Trim-based air to fuel ratio systems (Deltec- or Impco-based carburetor systems, high and low pressure)
2. Full authority gas injection systems (Tecjet), which are only suitable for low-pressure systems.
Load step performance and emission control:
In Australia 18 G3516 are equipped with full authority Gas injection systems (E3/E6 with Tecjet). Prior to upgrade, the engine managed to do 25% load steps. After conversion, the engines can take up to 50% load steps and any amount of load rejection. Eight of those units have the same response on natural gas as on propane and are able to switch between the fuels on the fly
These conversions are done on 8:1 and 11:1 compression ratio engines and steady state emissions are respectively 750mg/mn3 and 500 mg/mn3 of NOx.
Emission control and dealing with constant varying gas quality (landfill, sewage, bio)
Worldwide a large number of engines have been converted by engine OEM, Woodward or their dealers with E3/E6 products for operation on these gasses. In most instances a methane swing of +/- 4% can be dealt without a methane signal. For wider methane swings i.e. +/- 20% a methane signal is required.
Woodgas or also known as syngas is known to have very low energy levels and is continuously changing. LCI’s personal have successfully provided custom fuel systems for operation on these gasses as well.