Exam Question

### (a) Requirement for Pilot Injection in Dual Fuel Engines
Pilot injection is a fundamental operational necessity for dual-fuel (DF) compression ignition engines when operating on natural gas (predominantly methane). The primary reason stems from the significant difference in the auto-ignition properties of natural gas compared to conventional marine diesel oil (MDO).
1. **High Auto-Ignition Temperature of Natural Gas**: Natural gas has a very high auto-ignition temperature, approximately 580°C. The temperature reached in the engine cylinder at the end of the compression stroke, while sufficient to ignite diesel fuel, is typically below the level required to reliably and spontaneously ignite a natural gas-air mixture.
2. **Low Auto-Ignition Temperature of Diesel Fuel**: Diesel fuel has a much lower auto-ignition temperature, typically in the range of 200°C to 300°C. It is specifically formulated to ignite readily under the pressure and temperature conditions created during the compression stroke of a diesel engine.