Gentlemen,
The difference in DI and IDI is staggering. IDI's have a habit of being able to run a slightly lower quality of fuel while DI's have a thrist for a more refined fuel. IDI's have by their nature, burn slower, somewhat cooler and have slightly greater backup torque.. DI's burn faster and hotter... it's their nature. IDI's are always pintle injection whereas, DI's can be multi-hole or pintle... each having an advantage over the other. If you tamper with the piston in a DI engine you've done more damage than good. The combustion bowl in the piston was engineered for maximum swirl of the air so more of the air becomes intimate with the misted or atomized fuel being injected. Narrowing the bump clearance (distance from piston to head) is self defeating as you've managed to stop the flame front from propagating across the entire piston (the flame front will not propagate through a narrow slot.. you need to have at least .035 for the flame front to move freely across the piston). In other words, clever maching of the piston is needless and self defeating. Compression heat destabilizes the fuel. Think of it this way. From the piston pin down, engines are pretty much the same. From the piston pin up is where corporations spend substantial amounts of cash to make the enigne efficient... ie. piston, head, runners, valves, etc. all to get the maximum amount of swirl into the chamber... squeezing the charge doesn't do it all... it simply augments the swirl of the incoming charge.
In order to burn heavy fuel, you need to atomize the fuel... the heavier the fuel the higher the injection pressure you need to run. The pressure is nearly linear to the viscosity of the fuel. Makes sense, doesn't it? Next you need to heat the fuel before it gets to the pump.
Heavy fuel or alternative fuel engines are generally more robust to tolerate the longer burn time of a less refined fuel. Other issues are in the ring pack as fuel impingement is nearly impossible to stop in a heavy fuel engine (unburned, slightly burned fuel coming in contact with the cylinder walls). You'll also see a marked change in the power output. Something to remember, in a gas engine the fuel mingles intimately with the air thereby defining the engine as homogenous... naturally aspirated diesels manage to consume about 80% of the oxygen in the intake charge of air... the heavier the fuel, the less the oxygen it will react with.. the molecules are heavy.. they need to be destabilized through heat... a lot of heat.
